It clears the CRAP out of the temporary folders. If you're infected with something, it'll leave CRAP in the TEMPORARY FOLDERS, which is why you should run it as part of a malware removal process.Classic "it's how I did it when I was younger, and that's how it will always be" mentality.
I'm not saying you shouldn't use it, but mainly to regain free space. Clearing files which SOLE purpose is to speed up performance by making those files quickly available, is simply nonsense. (Also why it didn't help this person)