If you can breathe through your nose at all times its a plus and it also means you are in fantastic shape.

If you breathe out of your mouth while throwing punches that also means you are in your opponents range and you more than likely have a relaxed jaw. Bad things happen with a relaxed jaw.

I trained to breathe in and out calmly through the nose and out hard through the nose during a punch. It takes practice, but if you think about it the nose is on your face for the purpose of breathing and smelling. The mouth is for talking and eating.

I think us Americans need to use are nose more..