I stand up frequently when I'm just riding along. Minimal power, just letting the pedals fall.

On the other hand, I don't ride the super low gearing on the hills, so when I'm standing, I'm usually pulling up and putting a lot of effort into the climb.

Then, I guess it all depends on the hill. Less than 5%, and perhaps I can power down. Greater than 15%, and there is no resting without stopping.