Besides making a same-weight-bow more powerful than another with a shorter draw, a longer draw gives you better alignment. It's easier to get your arm in line with the arrow and your shoulders in line with your bow arm. Once an archer becomes accustomed to using a longer draw, they won't have to exert as much energy because now your bone structure is supporting the weight of the bow, and not your muscles. Of course, there's always a limit to this, as you don't want to overextend and get in the way of the string, but this is the only real negative to trying to find your full draw length.
Therefore a longer drwa is better because it gives you a power boost and improves your shooting.
