CCleaner, a product of Piriform, was known as "Crap Cleaner" way back when at the time it was first released.  It got changed to CCleaner when it became a commercial product.

Crap Cleaner is an accurate description of its overall function, though there are other specific ones such as the drive wiper that are part of it.  The main idea is that it goes through your system looking for files that it knows often get left behind when programs are installed/uninstalled, browser cache, etc., and removes them to free up space.

I hasten to add that it has a Registry Cleaner function that I don't suggest that anyone use.  I used to use it and it never harmed any machine I used it on, but as I've entered into more and more depth regarding the registry I have become convinced that the camp that says registry cleaners can unintentionally introduce many more problems than they solve is correct.  Just because it has the function is not a good reason to use it.
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Brian

Here is a test to find out whether your mission in life is complete.  If you’re alive, it isn’t.

    ~ Lauren Bacall