The multi-user (MU) feature has been rolled into core as Multisite ever since version WordPress 3.0.
It is ideal for a central system administrator to set up a large network of blogs with one installation. The sites in this network have different URLs.
Individual, separate site administrators are able to securely manage their templates and settings without affecting the other users.
Another scenario is a developer having all themes and plugins at the ready to create a new website for a client. The complication then becomes the transferring of all the content to the client’s base of operations.