I'd say most of us these days don't "need" the program for anything, but many of us prefer to keep our disk drives as free of "deadware" (which is what I call the myriad files and folders that are orphaned out there from installs/uninstalls, caching, etc.) as we can.
Tools like CCleaner do a marvelous job with getting rid of those files quickly safely, and easily.
I can also say I really prefer to use it to clear browser cache, whether for a single browser or all of them that I use. The full browser cache clearing process under Chrome when you choose "from the beginning of time" can, and often does, take ages. I can do an entire CCleaner full cleaning run in well under the time it takes Chrome to clear it's own cache.
I also love it when I want or need to tweak Startup programs. It makes that process much easier than Windows own tools do.
Brian AKA Bri the Tech Guy (website in my user profile) - Windows 10 Home, 64-Bit, Version 1809, Build 17763
Presenting the willfully ignorant with facts is the very definition of casting pearls before swine.
~ Brian Vogel