The idea is essentially to have a username for everyday use and one for Sunday best (or in this case system administration).
Terms allows you, as a system administrator, to attach Security Categories (SC) to various lookups to either control their visibility or to hide them away because they are no longer in use. This is normally done by attaching a Level 7 SC to the lookup so that only L7 users can see them by defeault.
This means that, as a level 7 user, all these old lookups are still visible to you ... A solution to this is to use the SUPER user account for System Administration (i.e. the L7 stuff) and to set yourself up with a personal Security Profile (SP) that is L6 by default but give yourself access to any L7 stuff that you need.
Because your Profile is now L6 you won't see any Lookups with L7 SC's unless you've specifically given yourself the relevant SC in your profile. You give your profile access to all the security areas that SUPER would have by default but still keep all those now unused lookups out of site.