Employee turnover in most organizations runs high. So unless you run a small shop with a stable user base, you need to learn how to clean up after an employee leaves.
Too many so-called system administrators do not understand the stakes involved when they manage users. Disgruntled former employees can often cause significant trouble for a company by gaining access to the network.
To remove a user, you need to learn to manage all of his or her files, mailboxes, mail aliases, print jobs, recurring -(automatic) personal processes such as the backing up of data or remote syncing of directories, and other references to the user.