The msdb database supports SQL Executive and provides a storage area for scheduling information. The msdb database is backed up in the same way as user databases and should be dumped regularly and frequently.
It is important to make backups of msdb regularly. This database is modified by such things as the tasks that you schedule from the Task Scheduling window, the automatic backups you schedule from the Database Backup/Restore window, and all replication tasks (which are automatically created as necessary, if the server is configured as a replication distributor).
Because the setup program installs msdb and its transaction log on separate devices, you can perform both database and transaction log dumps for msdb.