Might be wrong, but in previous versions of Moodle, the front page was considered a course. When one made a backup of the front page, one did get all users in the system (maybe due to authenticated user role), front page items, but not all courses, etc.
As far as backups go ... would highly recommend backups at both levels ... site and course. The courses could be backed up using auto and the site (depending upon your situation) could be scripted and cron'd. In both cases those backups are stored outside of Moodle directories. Restoring would require some manual labor.
If doing both, one can restore only the piece that one needs ... no more .. no less. That, I think, would be especially true of a larger site involving more than one teacher/class.
Best to have some backup rather than nada.
My 2 cents! 'spirit of sharing', Ken