When I draw from a live model I almost always get a better sense of movement, which muscles flex and those that relax for a pose, and how weight compresses the fleshy parts. I've always had a little trouble with foreshortening, as well, and so I try to draw the model from an angle in order to "work out" that part of my weakest drawing muscle.
I think what happens is I get used to my own visual shorthand, the lines I use for the abs, for example. I like how they look and so I use the same lines repeatedly. Not that I have a problem with doing so but with life drawing I have the opportunity to see different shapes in the body and maybe come up with a few variations on my little shortcuts.
So, the drawing above is Josh again. The Hockey model, etc... And, yes, I actually had him wear clothing for a few of the drawings.