Back about 10 years ago overdraw where, for a lack of a better word "in". An overdraw bolts up to the riser and has a arrow rest as much as 5 or 6 inches behind the riser. I'm not an expert on overdraws as this was just when I was getting into the sport but I believe that by adding one is shortens the brace height making the bow more susceptible to torque. I'm sure the guys in the tech forum are more qualified to answer the question than I am but I'm pretty sure this is correct.

It dose allow you to shoot a much shorter arrow resulting extra speed.