My experience is that on several occasions a malicious registry entry was eradicated by CCleaner. Tested this prior to and after running a scan by one of the better known anti-malicious programs. I consider this a fix, I also consider cleaning up any preventable problem before it becomes a problem to be a fix.
My business customers have a license, my residential customers may have a paid or free copy. I don't install it, I only recommend it and use it if it's already installed. Personally I use the paid for copies.
I've been using CCleaner registry cleaner since Win 10 first arrived on the scene. No issues as of yet and I service hundreds of computers in my business, both residential and commercial. It is fixing things unless you don't want your registry cleaned.