It's often taught that hitting in the center of the racket is the key to the game. But the top pros don't do that. They hit towards the bottom of the racket for topspin, and towards the top of the racket for volleys or slice. The racket will have much more stability this way, with the force only on one side. Topspin forehand, bottom of the racket; backhand slice, top of the racket.