Um, I no a cruncher so perhaps I shouldn't comment, but leaving a computer running unattended does carry a slight fire risk. Laptops run hot and desktop CPU cooler fans can fail leading to overheating and PSU's can literally fail and catch fire.
I know we leave fridges, clocks and other devices on whilst we're out but they're designed to run cool and safe, I would never leave a computer on while I'm not home.
I know it's only a slight risk but...