Originally Posted by Arainach
You don't NEED to run the Built-in one (or a 3rd-party); since Vista defragging has been done automatically behind hte scenes on schedule. Also, I've never understood the point of Registry "cleaners". Everyone assumes the Registry "slows down", but I've never seen any evidence of this.
When you have run a Windows installation 2+ years without reinstalling or cleaning your registry and still have it running well, you can make that claim, but I doubt you have done so.
As I said, the built in defragger is not very thorough, weather it's run manually or in the background doesn't make any difference.
Sure it does keep your files defragmented, but it doesn't compact the files at all, they remain spread out all over the disk.
Edit: Ccleaner also gets rid of temporary files, Windows often "forget" to delete a lot of these files, finding and deleting them manually is a pain, same goes for the registry.