The frequency for your database backup depends on the usage of your database.
If you are regularly updating or entering data into your database on the daily basis then we would recommend that you backup your database daily.
If you are making changes your database sporadically throughout the week, then you may prefer backing up your database on the weekly basis.
Backing up your database regularly protects yourself from losing data in the event that something happens to your computer/server. The more frequently that you backup the database the better chance you have for recovering lost data.