Does OS X Have An Inbuilt "Self Cleaning" Feature? Does OS X have an inbuilt effective "self cleaning" feature/mechanism. If so does it need to be turned on by default, and how often does it take place, (or is this something that is determined by the user).

Is it advisable to use apps such as CleanMyMac or CCleaner for example ? (or are they more harmful than good).
Applications such as CleanMyMac or CCleaner are unnecessary for your Mac. They can clear certain caches or preferences that can interfere with the proper functionality of your other applications - they'll be recreated anyway the next time you use the software. Unless you're in dire need of extra space on your hard drive, I wouldn't suggest trying to erase caches using cleaner applications. If anything, invest in an external hard drive and move some of your larger files over.