Why wouldn't you if you have free power? If you simply make sure your rig doesn't overheat, every $ is profit ( if you weren't going to do anything anyway with the pc's.

600 H/s would get you ~ 62$ a month, which could be a lot depending on where you are from. See https://www.cryptocompare.com/mining/calculator/xmr?HashingPower=600&HashingUnit=H%2Fs&PowerConsumption=200&CostPerkWh=0.0

That's ~720$ per year. Might not be much, but depending on the effort you need to put in, it might just be worth it.