This is actually very good advice.
If you make a mental connection between your intended speed, and the length of
your followthrough, you may find speed control to be easier, especially under pressure.
Use a long follow through for some shots requiring extra force or cue ball action.
A shorter one for stunning or quick-drawing or punching the cue ball short distances.
It's not that the followthrough literally controls the cue ball, obviously your cue can't do anything
once the cue ball has left the tip. But it's sort of a visualization trick that can make speed control
easier and more reliable for you. When you mentally rehearse a shot and imagine the outcome
(which everyone should be doing on every ball)... it's easier to imagine something you can
actually see. Like where your tip ends up when the stroke finishes.
Whereas 'visualizing' swinging your arm faster or slower is not so easy.
These visualization tricks are very touchy-feely and not related to physics or mechanics,
but they can seriously help your game. I recommend people keep an open mind and try it.
I already know it works because I use this on shots where the right speed is important.
It kind of sucks that SJD has decided he's going to follow CJ around and take little potshots
at his (legitimate) advice and turn a potentially useful thread into another stupid cartoon battle.
And others (you know who you are) should not necessarily dismiss a tip like this
just because the guy making it has been known to sell DVDs.
I'm not saying it won't work. Anything will if you want to bad enough. But it is like teaching someone to reach around your back to scratch your elbow. Sure, it works, but why would you do that? Why make things harder to do instead of simpler?
I don't, and never have dismissed anything said just because it's being sold on a DVD. I do dismiss things that either don't work, or actually make the game harder than it needs to be. This does not add consistency, it takes away from consistency. Which is obvious just by the fact that he wants one to follow through different distances for different speeds. That's the opposite of consistency.