Move forward to cut off your passing shots and rob your opponent of time.
Your opponent has hit an approach shot and is attacking the net behind it. As you wait for the ball, you know exactly where you want to hit your passing shot. But why wait? You can attack the ball with your movement as well as your racquet. Think of a third baseman. When a grounder is hit in the hole to his left, he moves forward and toward first base so he has his momentum moving in the direction of his throw. This way he doesn’t have to throw as hard, and he cuts down the time the runner has to reach first base safely.
You can compare this to being a passenger in a car. If the car is traveling at 30 m.p.h. and suddenly stops, unless your body is anchored with a seat belt it will continue moving forward at 30 m.p.h. Likewise, when a third baseman moves forward, he and the ball are moving at the same speed and he doesn’t have to generate as much force to throw it to first base as he would if he were standing still. The same happens in tennis when hitting a passing shot. By moving forward even the slightest bit, the racquet will be moving at the speed of your body and you won’t have to swing as hard to generate the same pace. You’ll also get your body weight moving into the shot and cut down the time your opponent has to get in good volleying position.