How often are the profile settings backed up?

The profile settings are automatically backed up every 30 days.

Enable Profile backup in the policy

Migration needs to be enabled in the policy to ensure that a user's profile settings are included in the backup. The profile settings will immediately be backed up after the policy change and then every 30 days after that.

See how to Enable User Profile Backup

Why are the profile settings only backed up every 30 days?

1. User profile settings in general do not change very often, so most of the settings will available for restore.
2. The User profile settings backup is quite sizable (anything between 400MB and 800MB).  If this is backed up daily then there may be a negative impact on the user experience.