prevent? Do you mean as in doing a specific technique?
At a point your power is disruptive and your hands do everything you need without much overt body movement. If you were trying to make a waza "shape" you would have to withdraw power to fit the shape, otherwise you would just control them and ruin the "shape" of a technique.
The same thing applies to weapons kata. When they touch your sword-their hitting transparent power-the ground is present in the weapon and a movement will launch them or cast their weapon without much effort. In and of itself it is disruptive to kata.