We recently setup an Archive space with "view only" permissions for all users. Being the parent space we could move spaces under it, when they are identified for decommission. Ideally, there would be an easy (one click) way to force the parent space permissions upon all child spaces as they are moved there.
After some searching and subsequent support help http://www.jivesoftware.com/jivespace/message/154022, it's my understanding that each moved space into the archive, must have its permissions set to inherit the parents permissions. Example: moving a space with 20 subspaces into the Archive. Each one would need their permissions changed to inherit. In my view this isn't ideal for the admin.