The premise of the lower stance is for greater power and small target when being attacked. To develop greater power in punches and blocks, one must learn to move their hips first followed by the punch or block. By moving the hips a fraction of a second before your technique, you will accumulate greater force through the torso leading the arms to the target. If your hips are stationary while punching and blocking, you only have the power of your arms behind the technique. If you use the torque of your whole body, through your hips, you will not only have a stronger technique, but a faster one as well.
Breathing is the most fundamental principle of life.
Without it one cannot exist. The same follows through to Karate. Anyone who has taken a basic Karate class will know that you inhale fully and deeply before a technique, and exhale completely with a sharp focus at the moment of impact. Needless to say, it doesn't work very well. Not only does it restrict your movement by bringing air into your lungs, causing them to expand while moving, but it also leaves you vulnerable should someone strike you in the diaphragm area.