Anything that scans your registry with its own database and tries to decide what entries are good and bad?
I agree with you there. I would never use a product that purports to be an expert in third party software, especially when it comes to the Windows registry. Norton 360 is not a Registry Optimisation application, which is an entirely different beast to a Registry Clean-up application.
However, Norton 360 doesn't appear to compare to any internal database. It simply checks if the records in the registry refer to software that actually exists. If the software has been uninstalled, but the registry records still exist for it, then 360 will delete them. It also works for file associations, for example, where a program has associated itself with a file type, then not reverted that setting when it was uninstalled, 360 removes the association.
While a clean-up may only save a few bytes, when I install and test many applications for a period too long to simply be able to use a Restore Point to remove remnants, all those records add up. Windows still checks many of them at boot up time, slowing the system if it tries searching for associated software. Not by much maybe, but a little.
For example, I just ran it for the first time in quite a while, and it found and deleted 59 entries. Despite the fact that I had uninstalled MC18 ages ago, 21 of those entries referred to MC18, mostly invalid commands entries and missing icon files. MC20 still works fine on this PC, despite those key deletions. There were some invalid ActiveX/COM entries, Logitech references to older Java jar file versions, file associations with uninstalled trial software, some outdate Adobe keys changed by updates, and so on.
Granted, things have improved, but when 360 finds something to remove, I can typically recognise what it is, and know that it shouldn't be there any longer. I guess I just like to keep things tidy. For me, that is added value. But I guess the old adage of "If it ain't broke, don't fix it" would apply to most Windows users.
BTW, I am just a 360 user, and have no association with Symantec, in case anyone was wondering.