Originally Posted by corners
You should check out David Bailey's footwork analysis. His analysis shows that there are four or five legitimate and commonly used footwork patterns - or "moves" as he calls them - where both feet are off the ground. As he explains, what "move" you use to hit the ball depends primarily on where the ball is and what recovery steps will be necessary to get you back into position after hitting it. On wide balls there are two moves that are commonly hit with both feet off the ground. On very deep balls that push a player back there is also a move hit airborne. And there are also two airborne attacking moves - one at the baseline used to hit high balls aggressively, and another used to move very quickly toward short balls, where the intention is to continue on toward the net. In all of these moves, I believe, jumping is not necessary to hit the ball, per se, but is necessary to hit the ball AND transition quickly from the act of hitting into the proper recovery steps that bring the player back to the center of the court.
The most basic of the moves all good players use, however, is what Bailey calls the "step down", where a player steps down into the court on a fairly low, short incoming ball and hits with a neutral stance before stepping through with the outside foot and then recovering to the center. If I had my choice I would use this move on every ball. The front foot stays down, the center of gravity is low and centered, everything is very calm and grounded. But rarely do we get nice balls that land somewhat short that we have time to step into, unless we're playing below our level or just rallying.
Tennisplayer.net has a very good series of articles by Bailey where he explains each of the moves, which are illustrated with John Yandell's high speed video clips of pro players. Each and every move is used in nearly every match by nearly every pro player. Once you are familiar with these footwork/hitting patterns you start to see them everywhere, even in vintage tennis footage. Rod Laver's dynamic footwork had him leaving the ground on nearly every point. I don't think it's necessary to practice the moves in a regimented manner as Bailey proposes, but just being aware of them and what can be accomplished using them is eye-opening and has changed my understanding of footwork immensely.
In addition, using proper volley technique you will hit the ball during the brief moment when both feet are off the ground, right before your front foot lands. (Reflex volleys when stuck in position are an exception, of course.)
So yeah, it's OK to jump, but with a purpose. Which is why it's a good idea to take up jump roping or some other bouncy exercise, which prepares your legs, and especially your feet, for such dynamic and explosive motions.