More draw weight allows you to (or, more appropriately, mandates that you) use a heavier arrow. A heavier arrow flying at a high speed makes more kinetic energy than an lighter arrow flying at the same speed. You don't need all that much KE to hunt whitetail and turks. With the cams in most of today's bows, a 40 lb draw will fling the arrow plenty fast enough for shots out to 25 yds or so.