I leave my computer on for three reasons:
1. I don't like waiting 20 seconds for it to boot
2. I don't pay utilities in my apartment
3. And most importantly, the front power switch is about 6 inches from the wall it's facing in my closet. So I have to bend over through my clothes to turn it on or put a CD in. Yeah, it's a pain, but my room's small enough that I thought it best to throw the computer in the walk-in closet