I seem to remember reading that Mark Selby moved up from being a jobbing professional to one of the real monsters on the pro snooker circuit when he shortened his stroke (although it is still one of the longer ones). [Edit - I should say that I cannot now find any evidence to back this up]. And Steve Davis said recently that the biggest improvements that most amateurs can make is to shorten their bridge.
It could be that some players have an overly long final backswing because they need the time during this phase to mentally prepare to deliver the cue. If so, then they might want to follow Allison Fisher's lead: she said that the biggest improvement to her game came when she slowed her backswing down. (Logically, this would provide the necessary final preparation time in a shorter stroke.)
