anyone know how registry cleaners work?

I wanted to know how registry cleaners work on a basic level. I found http://www.registrycleanersrated.com thats good but just wanted to know how registry cleaners worked before I download the program. Any tips? Thanks

Basically, every applicaiton takes and registers a really long number in the registry. Think of this as like your home address. If there are entries that do not correspond to proper home addresses or do not have home addresses assocaited with them, then a registry cleaner deletes the entry in the address. This is a very basic overview of how a registry cleaner works.