If we were birds we'd need really powerful pecs to power our flight motion. As it is the pectoralis major, the thick, fan-shaped muscle, which makes up the bulk of the chest muscle, is used to flex, extend, and rotate the humerus, the long bone of the upper arm. This powers throws, punches and grasps. The Pecs workout is designed to help you improve in all of this by making your pecs stronger.
Extra Credit: 1 minute rest between sets.