A lot of it is dependent on EA and how well their classes are made.
I would use it to correct the things I cannot tolerate. Things like CBs with linemen strength, OL with 72 strength and 82 speed, the problems with the speed trinity (ever notice how rare it was for a WR/CB to have decent ratings in all three of speed, acc, and agility? Usually it was 92/88/74. I would correct that to something like 90/88/86). And possibly bring the average rating down but that would require testing (schemes complicate matters, but that is a good thing)
Also real life prospects is something that is important to a lot of people, as Charter pointed out in his post.