|On laptops, sleep and hibernate are different. Sleep is best for short breaks up to a half hour and hibernate is much better for longer breaks and for overnight, turning it off is best.|
When you just close the cover, you are suspending to RAM and your system is continuing to supply a minimal current to the memory to keep it alive. If there is a tiny drop in the current, you will loose the integrity of the memory. With hibernate, your system is suspended to a portion of your hard drive so your system uses less energy from your battery and you are less likely to loose anything open or the ability to resume.
If you get into problems where the power button is not shutting it off or turning it on, remove the battery for 10 seconds or more and then restart it.
You have to be a little bit crazy to keep you from going insane.