I agree with sig and eww, there's no need to "clean" your hard drive. There are many utilities that claim to do that, but the things they do can harm performance or even damage your system, requiring it to be reinstalled. One popular gimmick is "cache cleaning." Although a corrupt cache can cause problems, that's rare (I've never seen it happen on any of my Macs), and caches are important to keeping your machine running fast. Frequently deleting them, which is all a cache cleaner does, is a bad thing.
Don't treat your Mac like a Windows machine, and don't install utilities that are the digital equivalent of snake oil.