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 (my website address is in my profile) Windows 10 Home, 64-bit, Version 1709, Build 16299
Here is a test to find out whether your mission in life is complete. If you’re alive, it isn’t.
~ Lauren Bacall