Ok, I been practicing hanging with a knee down.
Sliding your butt over and hanging really makes a faster pass
through a curve. It allows to shift the weight and actually not
have to lean the bike as far. Tires can only be leaned so much,
so if you get out on the side of the lean you can go faster without using
up the available tire patch and low siding. That being said, you can shift your
weight over without putting down a knee.
here is a real good ask Keith Code thread, the link takes you to a picture near the
bottom of a fellow pushing a bike down while he rides high, ie not shifting his weight,
Keith address it later on.
http://www.ducati.ms/forums/showthread.php?t=14864&page=7&pp=10