The master database is one of the default databases installed in your SQL Server. If it were to become corrupted, your SQL server may no longer work correctly.
- Logins and roles associated with user ids.
- System configuration settings such as data sorting info, security implementation and default language
- The names of and info about the databases on the server
- The location of each database
- System tables that tell you: available languages and characters, system errors and warning messages the way the cache is used and several other things.
Backing up this table should be a part of your routine back up.