SwitchBack wroteMy straightforward rule of thumb: If it warms up you turn it off, if it stays cold you can leave it on. Good for safety, the environment and the gear itself (heat degrades electronic components).

Part B of that rule: let gear acclimatize before turning it on, to avoid unnecessary temperature stress. Usually says so in the manuals too.

There used to be a rule to keep anything spinning spinning (harddrives, fans, ...) but that’s outdated, because if you don’t turn them off then they will do so themselves nowadays