Height has at least 3 advantages:
1. Higher serving angles.
2. More powerful groundstrokes (it's physics: if you measure the speed of a straight "lever", the speed is greatest at its tip...and a longer leveler means more speed in the contact zone.
3. More reach on service returns.
Height WAS a liability for decades because it does slow movement. But modern training makes it possible for a Berdych, DelPotro, etc. to have enough speed to be successful.