1. Why would it even be useful?
It is generally instructed that it is a horrible habit to change your aim deliberately when down on the shot, due to your alignment being then thrown off, such that even if your shot picture looks correct, you'd most likely miss the shot. This makes sense, you have lots of moving parts in your body, and if you carelessly just move some of them around until it either looks or feels right, you will most likely not have a repeatable method.
Now, let's ignore other parts of your stroke that aren't relevant for this discussion (spin, power, elevation, etc.) and only focus on the sideways alignment, e.g. the point on the object ball that you will hit. Assume for a moment that there existed a method that lets you adjust this alignment when down, without hindering your stroke straightness at all, such that your shot image (and therefore your expectation) properly matches with what actually happens when you shoot. You'd obviously still have to know the right cut angle (have the right shot image), and have good fundamentals (straight stroke, etc.).
Even if this all were true, one could still argue that it is less effective to aim when down, due to the perspective of what you see being so different. I can see the merit of this argument, there are shots where I definitely think the shot image is much easier to see when standing up, e.g. blind backcuts to middle pockets, or when you are very close to the object ball. However, there would also be advantages to aiming down, such as:
- You no longer need to drop straight into the line of the shot, and keep that line in order to be effective. This is, in my opinion, the biggest benefit.
- On longer pots, the perspective of being down on the shot, can make it much easier to see what cut angle you are looking at, since the object and cue ball are closer to eachother in your field of vision.
- If you can effectively see the required cut angle (shot image) while down, this makes it faster to align yourself when down instead of aligning when up and having to carefully drop straight into that line.
Even if all of above were true, I'd definitely see arguments either way for whether aiming when up or down being better. There's clearly nothing wrong with aligning yourself the normal way, since almost everyone does it, especially the pros, but I found this method useful, so maybe someone else here will aswell, perhaps if they are struggling to achieve excellent precision with the typical method, which I did, and improved my accuracy by a huge amount after switching to this type of alignment and practicing/improving the method for a while.
2. The method I use
My stance and stroke are similar to the typical snooker player. I have four contact points on the cue (bridge hand, grip hand, chin and chest), and execute a straight piston stroke without any up/down movement, slowly pulling back, pausing for a moment and then going through, keeping everything except the cue arm as still as possible during the stroke. (BTW, I find that keeping the cue on my chin and chest at a constant light pressure at all times during the back and forward stroke helps me a lot to execute a clean piston stroke with close to no effort. When I didn't have my chest on the cue, I couldn't avoid having slight unwanted up/down movement, but this isn't really relevant for this topic, so I'll move on.)
Now, for this alignment method to work, you have to have your cue touching your chin. Having it on your chest might not matter, but for me it definitely helps a lot.
(The actual method description starts here)
Let's think about what you are seeing when you are down on the shot. There's the object ball, the cue ball and the cue stick. For a succesful alignment, the following must be true:
1. The OB/CB overlap must be correct (right cut angle)
2. The tip of your cue must be aligned to the right point on the CB, and at the right elevation (Let's ignore swooping the stick etc, and just assume you can hit the CB wherever you want to address it)
3. The backhand must be aligned (sideways) such that the cue forms a straight line towards the contact point on the OB, or in other words, makes the executed shot match the alignment that you see in your shot image.
1. and 2. are trivial even if you had no idea what you were doing and started adjusting your aim when down, since you can easily see if the overlap is correct, and after that you can just re-align your tip to point at the correct point of the cueball. However, step 3 is the tricky one, If you drop down into the shot normally with a slightly wrong cut angle, do 1. and 2. to fix it the way I just said with no extra thought, you will most likely no longer have the right backhand alignment.
This has an easy fix though. If you keep the cue touching your chin at all times during steps 1. and 2., (always in the same sideways position, e.g. center of the chin or 1-2cm to the left or the right, this depends on your vision center, etc, just find whatever works for you),
AND keep your head at the same angle relative to the cue, your backhand will automatically be aligned properly, causing all three requirements for a succesful alignment to be true.
(If you are unsure as to why this is true, you can think of the correct point on your chin as a "fixed point" that always aligns the stick to the same place relative to your shot image, due to your eyes always being at the same place relative to that point in your chin, assuming your head is rotated the same way relative to the cue.)
Let's focus a bit more on the second part, since keeping the cue on your chin on the right spot is pretty trivial, but having your head always be in the same angle is not.
There are three types of rotation that your neck can do. Out of the three, pitch doesn't affect the sideways position of the correct point on your chin, but roll and yaw do. Using this method, the main cause of missing a shot (due to the method, ignoring bad fundamentals, having the wrong shot image etc.) would be having unwanted roll or yaw in your neck. I personally eliminate these by always stepping into the shot the same way (so it would ideally just not be rotated in the first place), and during my time spent doing feathers and aiming, making sure my head looks (with peripheral vision) and "feels" like it doesn't have any roll or yaw. For me, yaw isn't an issue, but roll can sometimes be, and it's the one to look out for. When you are touching your chin with the cue, you are pretty low with your head, and it can be tricky to keep it perfectly straight in that rotation, but it's possible and with some practice you can eliminate that issue well. To be precise, it doesn't even have to be "straight", it just has to always be the same amount, which you can then compensate for by having the point on your chin be slightly off from your vision center to cancel the effect out.
So, to sum it up, here is my "shot process" summarized for normal pots (no kicks, caroms, combos etc. those can be very different in some parts), I will also include parts that aren't relevant to this method.
1. Shot selection, figure out the shot that you will commit to. This includes tip position, full path of OB and CB, etc.
2. Visualize the shot, and give your subconscious the necessary information, so e.g. if it isn't a trivially easy shot, go briefly stand over the potting line to have a better view of the angle.
3. Chalk the cue, stand behind the shot at the right distance, do a few air strokes.
4. Drop down into the shot (always with the same way, which is not really relevant here so I won't go into it, but I try to make it as similar as repeatable as possible) roughly in the right alignment without any conscious effort spent into alignment, so I'd never be off by multiple centimeters, but millimeters won't matter as I do my proper aiming when I'm down.
5. When down, I will start aiming, I have a certain set of eye patterns/practice strokes that will vary a lot by feeling, since this part of the process is very subconscious. I simply know what I want to happen to the object ball/cue ball, and let my subconscious align my vision to the right spot to make that happen as well as it can. There's lots of mental tricks I use to maximize the subconscious mind's potential here (to stay out of it's way, how to not interfere with it, etc.)
6. Once the practice strokes are done, I trust that my subconscious chose the right aim (shot image). From now on, I focus on everything being perfectly still. Due to the main method discussed in this thread, I know my cue is also aligned properly to allow me to execute the shot, even though I adjusted my aim (shot image) when down.
7. IF something looks or feels wrong, I will stand up, and restart everything. But this is pretty rare, and it is a fine line to be too careful, for me it doesn't help to start analyzing visually if what I see looks correct at this point, since my subconscious knows better than me anyways. I find it better to just trust it if it feels right, and take the occassional miss, instead of paralysing the whole process and getting into my head due to the fear of being incorrect, and trust that the results will improve better like that in the long run.
8. I pause, shift my main focus to everything being perfectly still and start executing the back stroke, looking at the OB but focusing on the image of the cue stick/ball in my peripheral vision.
9. Pause at the back.
10. Smooth stroke keeping everything else still, visually focusing on the OB as a whole, but still also focusing on the image of the cue stick on the peripheral vision. I don't have a "contact point" on the OB that I try to push the cue towards, I find that just focusing on the OB and cue stick as a whole lets my subconscious direct the cue in a straight line more effortlesly.
11. Stay down for a while, observe the shot.
