This computers in mine and my brothers room so can't really.
Power bill would also become a problem I think, but I don't tend to think of that as a problem mostly, but I guess it would add up.
The only time I'd leave it on all night though was if I was doing a render that I couldn't switch off and it was going to take longer than expected, but for that, I'd probably switch on the slower computer downstairs which doesn't use much power, and give it that to do for a few days or more.