The answer is, of course, virtually everyone. I believe truly, though, that it is the average player who benefits the most from fitted clubs. The normal athlete is the guy or gal that works for living and golf is not their full time thing. To play an ill-fit club that requires compensations and inhibits talent makes the game harder than it already is. I mean that compensation and manipulation are what the body in motion must do to hit a ball straight to the target if the clubs are ill-fit.
Every woman knows that changing from flats to heels requires a change of motion, balance and gait.
Sports like baseball and tennis offers similar stories. The weight or length of the bat, the construction and stringing pressure of the tennis racket all affect the player's feel, motion, sensory perception and performance. The player will adjust timing and body position, grip and length of the back swing and other motions to find a way to perform adequately. As a teacher I can teach a player how to compensate or even to contort the body to make his or her clubs work, but morally I would rather fit the player to clubs and educate the player as soon as possible. A. Learn properly, in fact.