In the "tools" section, there's a "disk analyzer" showing which files are taking up how much space. What would be the result of deleting all the "other files"?
The general results of deleting "all" of anything via any tool blindly will likely kill a machine. One should be very judicious when using a powerful tool that lets all of one thing be deleted (not just ccleaner, but within ccleaner examples of when not to remove all include duplicate finder, disk analyzer and registry section)