I've seen a lot of teenagers riding BMX bikes recently.
It seems that most if not all of the guys I've seen riding their BMX bikes around the streets, car parks, local parks, etc have a frame that's really small, and a saddle that's as low as possible. It looks like the rider's knees are above their waists for much if not most of their stroke.
One of the local parks has a dedicated BMX track with actual racing taking place on it. When I watch those guys they never seem to have their saddles all the way to the bottom.
The thought occurred that it might have something to do with trick riding but none of the kids with bikes set up like this seemed to actually be doing tricks. They'd just be riding the bikes normally or even just sitting on them outside shops. Their bikes also didn't seem to be set up with trick riding in mind, most of them didn't have those bar things projecting from the wheel hubs for the riders to stand on.
Is this really low saddle something they're doing to be cool? Or are there some real tangible advantages to this seating position?