I can't even imagine shooting without one. My sling and how it is adjusted is as important to me as any other part of my bow. Without a sling there is no way I can follow through. You don't need to have one, but then in my opinion you're not shooting proper form. I want the bow to fall gently forward without any grasping of my hand. I don't hold my bow, it rests in the V part of my hand only my index finger will touch the riser. I make my own slings, and pay a lot attention to the adjustment. I'd rather shoot without a stabilizer than a sling!

http://www.youtube.com/watch?v=e9Rtd97cbZoCheck out the position of his left hand, and the follow through. His bow was a little out of vertical for me. This is the way I let the bow fall forward, there is no possible way to torque the bow using this form.