According to Krishnamacharya , practice and knowledge must always go together. He used to say, practice without right knowledge of theory is blind. This is also because without right knowledge, one can mindfully do a wrong practice.
Breathing is important in the practice of meditation because it is the faculty in us that is simultaneously voluntary and involuntary. You can feel that you are breathing, and equally you can feel that it is breathing you. So it is a sort of bridge between the voluntary world and the involuntary world — a place where they are one.