In one sense it really doesnt matter, as long as the arrows fly well. Some people have arrows only an inch longer than their draw, others go a few inches. Longer arrows make it easier to aim with the arrow tip.longer arrows are heavier. Shorter arrows are easier to carry, and its easier to find short shafts. Changing arrow length will also change dynamic stiffness, which greatly affects arrow flight. Self bows tend to need arrows that are not too stiff especially at shorter draw lengths, so, longer arrows would help achieve this . This stiffness is also affected by point weight, arrow spine, and other factors.