One of the best explanations on that I heard in recent times was from Matt Kuchar who just came up off the Nike Tour (now Nationwide). He said the guys on the Nationwide tour hit it farther than the Big Tour and they also aren't quite as good at avoiding mistakes and getting the ball in the hole as they are on the Big Tour where they generally hit it shorter. Obviously his message or implication was they don't try to hit it as far on the Big Tour for obvious reasons.
A perfect example of that belief and perhaps reality may be proven in the career of Davis Love. When he first came up nobody could believe how far he could hit it and did hit it but for a year or two he wasn't making any money either. Then he toned it way down and started winning. He probably toned it down too much for a time because he seemed to step it up a bit and won even more but generally he never tried to hit it again as consistently far as he did when he first came up.
As an interesting update on ultra-distance, most of you will remember the reporting I did on here around the US Amateur at Merion regarding the length of Long John Hurley, the 18 year old Nebraskan.
Well, the other day I talked to the tech guy who does all the testing in the last few years at Opens and Amateurs and I asked him how that ball speed of Long John Hurley's stacked up in his stats. He said the USGA Tech Center testing had never seen a ball speed that high in real life!
(on the way down the fairway Long John said; "I didn't really catch that one--I cut it a little.")