Verified answer

No, diskcleanup scans your computer for temporary and unused files like your internet history or recycle bin. It is ok to delete them

it depends what files, it wont delete required system files, it will only delete files you don't use, i think including internet temp files, i recommend getting ccleaner, its very handy, i can notice increased performance instantly with the registry cleaner www.ccleaner.com, trust me it has absolutely no spy-ware or ad-ware included what-so-ever, and i also recommend doing a defrag, O&O defrag is an excellent defrag tool, if youre not very computer saavy, it takes all of the files and rearranges them so your computer can find them easier therefor your computer will run faster opening file wise, not processor speed, hope this helps

It doesn't delete them! It just compresses old files that you haven't accessed in a while. Just don't do it. It will not save that much room.