I have used ccleaner for several years now including the registry cleaner.
No problems that I can remember.
ccleaner seems to update fairly often so I tend to hold off on updates for a while just in case one of the updates proves problematic.
Also I have become a bit more skittish about the registry cleaning. Not sure about the benefits to risks balance.
Best, I think, to leave well enough alone aka "if it ain't broke, don't fix it".
Always back the registry up first as recommended if you do decide to use/apply the cleaner.