How important is it that you keep your knees bent? Critical or depends? I used to keep my knees 'slighly' bent, or flexed.... but my coach now has me keep my knees much more bent. Almost a head below with my posture. Its going to takes months of shadowboxing, bagwork and sparring for it to become natural. And it really works your quads.
But I have found out this: If you are advancing, you can cover more ground quicker. And for headmovement, it MUCH easier, since you move the head with the feet and your knees are already primed to move. AND many times you are already 'sitting down' on your punches and they may be more powerful. AND it makes it easier not to bend at the waist, since again your legs are already primed?