SQL Server Offline database
When you want to remove access but not DROP the database

Example 1: migrate one database to a new installation


Prepare new server
Backup/restore to new server
Update application connection srings
Take DB off-line on old server
Test thoroughly
Drop DB on old server


Without taking the DB off line, you limit rollback options

Example 2: Cleaning up a messy SQL Server (e.g. developers created DBs)


Take offline, see who calls...