(Following compliments of Pete James and besides just covering sitting also contains thoughts on boarder attitude.)

"Snowboarding takes a lot more out of ya than skiing. On skis you can widen your stance and coast on flats, and take it easy. In snowboarding, there is no taking it easy. You always have to be in a carve, toe or heel edge. If you flat board it, that is when you are likely to catch an edge and do a real hard body slam fall. These hurt. On traverses, often boarders have to ride on one edge for a long time. It is like trying to stand on your tip toes for a continuous period of time. It is quite fatiguing, even if ya flip and ride fakie to relieve it. At any rate, this exhausts riders, and makes them need to rest more than skiers. That is why we sit down alot. Also freestylers like to sit and plan there next trick, or air, or what ever. All skiers and snowboarders should always rest on the side of the trail, not under a lift, and so as to be seen from above. A lot of boarders, never have taken a lesson and been told this safety info. A lot of them are younger and just are not tuned in or aware.

Pete

PSIA ski and snowboard instructor

Joel Tornatore adds:

It's very difficult to stand still on a snowboard. If you want to be stationary on a slope, you would have to balance, much like a bicyclist balancing when stopped at a stoplight. Because the bindings don't easily release, about the only way to stay still is to sit.

Editor: On a personal note, I attended a snowboard camp where one of the instructors (Chris Karol) who had been a pro for 10 or so years never sat down. In the 2 days I was there I never saw him fall or touch the snow with any part of his body except his hand. If he had to stand in one place for more than a couple minutes he'd unbuckle his rear foot (he was wearing hardshells). When he came to a stop he'd sort of dig his edge in and balance there, regardless of how steep the slope was. The snow was pretty soft so that helped. The point is, using strength and balance, it is possible not to have to sit down.