Volume Shadow Copy is kinda neat.

(Layman's explanation.)

It basically makes invisible (the system doesn't inform you of them) clones of files that you have manipulated in some way. That way you always have a backup of something if you 'accidentally' do something.

Theory is that it will clean itself on its own as you require the disk space.

Example..

I install World of Warcraft + expansion + updates for 7 gb, but I only report 4gb free on my 250gb drive.. The 3 gb I "don't have" magically appears because the shadow copies in that 3gb chunk have dissolved.

*Puts on an Asbestos suit*

Ok, now grill me for not giving a 100% accurate tech answer.