Oh, don't forget it's a good exercise. Your legs stay moving, keeping em warm and flexible. Blood pumping through that region. I am pretty sure circulation improves in other places, too. And, all these cardio-vascular exercises without much impact to body (assuming we aren't talking about going professional and competing in races and stuff), ... and without having to put on a lot of miles (just commuting even), I suppose. It probably isn't enough to really lose weight, but it's enough to keep em off once you get them off.