On larger STE systems (100+ exts) it becomes difficult to keep track of all of the extension, hunt groups and IVRs created. When one piece changes, it is hard to know if you need to update any other areas.
Example: UserA at ext 1001 left the company and new hire UserB is going to take over the old extension 1001. When x1001 is currently in multiple hunt groups for sales, admin and support as well as being assigned to the option# in a few IVRs. When UserB took over this extension, they are now getting calls that they do not know how to handle. From an admin perspective, I have to ask to the client for call examples (client frustration rises), trace the call which takes time (client frustration continues to rise) and bring to their attention that they never asked to have this extension removed from any of these hunt groups or IVRs and I am shamed for not having mastered the art of mind reading. Days go on and I continue to get call examples, each time finding new hunt groups or IVRs that the ext needs to be removed from.
Of course the above example is fictional, if it were me I would query the db and find all DIDs, hunt groups, IVRs, queues, etc that pointed to that extension; however if there was a summary tab or 'Member of' tab in the extension settings that shows all of the hunt groups, IVRs, queues, DIDs, feature codes, etc that point to that extension then any level user could easily see what objects need to be modified/changed.