I used to use what I call, contact point to contact point aiming. I put in some quality time using manual CTE/Pro One, actually manually pivoting and getting the mechanics down pat. As that progressed and I gained more confidence with CTE/Pro One, it morphed into Pro One, which is more of an auto-pilot form of the manual CTE/Pro One. As I used this, I seem to gain more precision with everything, my alignment, my cue tip placement, my aiming and now after many months of using CTE/Pro One I hardly think about the steps and do most of my aiming standing up. I think I am back to what some people might call instinctive aiming, but the reason it seems instinctive is that my precision has increased as a direct result of learning CTE/Pro One.
I've taught individuals how to use CTE/Pro One on a limited scale and some of them are astounded by the accuracy that they can pot certain shots.
I am in the process of learning the SEE SYSTEM now and will "see" how that goes. My initial impression is that the SEE SYSTEM by Ekkes is similar in some ways to CTE/Pro One.
If a person can simply see the sighting line and the correct aiming line and place their bridge hand in the perfect spot for potting the object ball, they have no need for any aiming system. For those that have some trouble doing that, the different aiming systems can be of GREAT BENEFIT.
Like Johnny mentioned, there is a certain placebo affect gained from the initial learning of an aiming system but it is more than a placebo. Aiming systems make people pay attention, some more than others.
Some aiming systems seem to be complicated to some people and for others it is easy to assimilate. Personally, I struggled quite a bit in learning CTE/Pro One but in the long run, I believe it has made me a better cueist.