By holding your breath you will get "gassed out" very fast and have less power. Breathing is really about the most important thing you can do in almost anything except swimming or being in a room filled with smoke.

I used to do that the rule is three hops in the heart but then again you can mess up you blood rate and some martial art is to hold breath while practicing technique is say three hops in the heart or the movement of legs only.

No, oxygen is needed to fuel your muscles. So holding your breath accomplishes nothing.

No.