The benefit of the wall is that it's repeatable practice. YOU control how the ball comes back at you. This allows you to weave out kinks in coordination, technique, consistency, etc. When things go wrong in my mechanics, I go to the wall to work out those problems. It's awesome for backhand drills (just you try to find a player to give you consistent feeds. Most don't even have a backhand themselves.)
The wall has its purpose in tennis training: developing consistency through predictable repetition.
When their tennis really matters, Babolat Reps use a Wilson.