The primary goal of Database Mirroring technology is to increase the database availability. When enabled, every update to the principal database is immediately reproduced onto the mirror database.
There is a very Hot Term that is StandBy Server. The meaning of Stand By server that if your Current Server Crashed then this can be used as live server. During a typical mirroring session, after a production server fails, client applications can recover quickly by reconnecting to the standby server.
Database mirroring is a primarily software solution for increasing database availability. Mirroring is implemented on a per-database basis and works only with databases that use the full recovery model. The simple and bulk-logged recovery models do not support database mirroring. Database mirroring is supported in SQL Server Standard Edition and Enterprise Edition.
Database Mirroring is used in different Scenarios
When the Database Records are very much important mirroring is used.
Real time systems need database mirroring.
You cannot mirror the master, msdb, temp, or model databases.