Unless you're a highly skilled and knowledgeable user, it's really risky using any registry cleaners or optimizers of any kind.
Extra leftover registry entries don't hurt anything, and unless you are digging around in the registry, you would never notice them anyway. Best bet is to not worry about it. It can cause more problems than it fixes. I know for most people it's just the idea of the registry being as "clean" as possible, and it makes them feel better about their pc, but it really doesn't make a difference.