Just as one data point, the last time I ran Disk Cleanup, it hosed my entire Windows installation. The bug in question was documented as occurring in Vista, but wasn't fixed in Windows 7, and for all I know, still isn't:

http://www.winhelponline.com/blog/serious-disk-cleanup-probl...

I'm admittedly out of the loop, last time I used disk cleanup would have been Win7, I guess MS expanded it to do much more useful work?

On my W10 install, CCleaner usually finds ~1GB more than Disk Cleanup, not even counting browser caches.