Alot depends on a lot of things. For example how much data can you afford to lose, or better worded, is allowable in the worst case scenario? How big is your database? Is it practical to perform a full backup once a day or would once a week be more apprpriate together with differential backups and transaction logs?

These are questions you need to go through your documentation and company policies for in order to find the answers.

The system databases don't need much attention except when:

The MASTER database contains changed database structures.

The MSDB database has new jobs, packages etc;

The MODEL database has changed templates for database creation, required when restarting the instance so TEMPDB can be rebuilt.

TEMPDB is rebuilt every instance restart/start and does not need to be backed up.