It requires energy to take the cue back and it takes more energy to redirect the cue. Mentally (usually sub consciously) there's a calculation that must take place to equate the forward movement of the cue with the speed and length of the shot.
I like to practice exaggerating this technique so that there's a distinct forward motion of the cue......after all, we never hit the cue ball with our back-swing, it's just used to coil the cue back before the moment of release - or they say "the moment of highest tension".
There is one school of thought that the follow through doesn't matter because the cue ball is already gone. This may be true in one respect, especially if you just look at the stroke mechanically. However, from my experience it's vital to control the after contact movement of the cue ball WITH the length of the follow through.
This is what gives the player that high degree of touch and feel for the game that's essential for top notch performance under pressure......when you are in that "do or die" situation.
When I want the "after contact" movement of the cue ball to be exaggerated I exaggerate the follow through, when I want the "after contact" movement to be compat, then I compact my follow through.....even if I want the cue ball to jump slightly I'll use a "staccato type" follow through that creates that movement.
If I didn't have a very good understanding of how the cue moves FORWARD from the top of the back-swing I would not be able to play at the champion's level of performance. Whether a player is aware of it or not the follow through must connect to the "after contact" reaction of the cue ball....or you'll always be playing a "guessing game," and it really shows up under the pressure of a high dollar match or tournament.
The cue ball's reaction, at the highest level is a reflection of what the cue is doing......the more you can calibrate the cue's motion to coincide with the cue ball's "after contact" reaction the better off you will be.......this is one of the essential "differences that make a difference" in winning or just coming close. 'The Inner Game is the Teacher'