This is certainly true in the beginning of a game. Players claim to do this to warm up. However, in a busy confrontation there is no reason to spam any actions that are not directly contributing towards your endeavor. If you spam useless actions during a fight, your opponent who does not will best you.

In Smash? Sure. In StarCraft? I’ve never measured it, but I wouldn’t say ‘most’ by any stretch.

The game's been played competitively for more than 25 years now, people still earn their living plying StarCraft. You wont find a single one of them with APM below 200. Having their livelihoods and legacies depending on this, do you think they'd be repeatedly doing something useless instead of optimizing?

Anyways, I think you are missing the point that this thread is about active sitting. I imagine there isn't much difference to the meaning behind movement: movement is movement, meaningful or not.