It's probably better to leave your computer on idle for a while than cut it off right after you're finished. Though it will still create heat, things should cool off better with the fans going...
I cut all my computers off at night mostly because of heat and noise in my room. My laptop is the same, I don't care to leave it on all day, but I also unplug it most of the time. Then again, mine gets much more hot than most laptops out there... Heck, it has 3 fans!(2 in the system, one in the PS)