There is no point in using a "registry" cleaner whatsoever ...
Yes, some can be detrimental to your health, or more to the point, the health of your PC ... none, including CC will give you any "performance" enhancements unless you know of a website that can show me different, I'd like to see the figures.
However, CCleaner is a very nice little program that can help clear a lot of rubbish off your PC ... if it has a go at the registry at the same time, what the hell, go for it ... but because CC can clear other rubbish off your PC, that you will find difficult to even find, I for one, can highly recommend it.