I cannot speak for the gentleman in question but I can say that some shooters prefer the crisper release generated by a lower letoff setting. It can provide increased accuracy in some situations.

Though I have not checked it on either of the Bowtech single cams, in the past and on other manufacturer's bows that had a draw stop peg letoff adjustment the speed remained relatively the same because as you lower the percentage of letoff you are also shortening the valley and subsequently the draw length of the bow. The two sort of cancel each other out...or at least they did with models I tested in the past.