are you saying you don't think it necessary to get rid of temp files, cookies etc? I did my monthly clean up yesterday and got rid of 1.5 gigs of crap.
Temp files, cookies, and the like are not stored in the registry, so "cleaning" the registry will not remove them. Conversely, cleaning up temp files and cookies typically requires no changes to the registry. The only time the two are correlated are when files or other objects that are taking up too much space are pointed to by registry entries for active applications, and that's actually pretty rare—and can be fixed by simply deinstalling the applications in question.