Why do some walk their bikes across gravel?

I people walking a lot, but I've always just ridden over gravel
(parking lots and such). What's the motivation to walk or even carry
your road bike?

I guess with a high-end TT rig, if you picked up a pebble, it could
tear sh*t up between the tire and frame. Could this be it? I've see a
lot of standard road bikes being walked too.

I'd rather have my tires on gravel than my cleats.

Example from yesterday (TT bike):
http://www.cyclingnews.com/photos/20...uphine06-s3-01