Depends on the situation.
When I'm developing film, of course, I'm standing, moving about, messing with timers, beakers and so on. Not standing still.
At the computer, I feed a film holder into the scanner; if the scanning's going to take a while, I'll head off and so something else. If, say, I'm running an action on a heaping number of image files (like resizing a hundred or so big TIFF files to JPEGs to put online), I might start the action, grab my helmet, take one of the bikes and go for a few laps in the park. I get my ya-yas out and get some photo work done. Same thing if I'm making a lot of prints...I don't have to be there riding shotgun unless there's something espcially intricate or otherwise tricky happening.
IOW, Photoshop ain't making me fat. Or, at least, not any fatter than I've been. 😉
- Barrett