What information is backed up?

The standard backup (executed via Manage > Backup) includes:

• The entire database used by your MODX site, excluding the session table
• The active MODX configuration file in core/config/
• The various config.core.php files
• .htaccess

When a backup is executed as part of a remote upgrade, the backup is extended with any file that is different from the downloaded MODX version. 

This means that this type of backup is NOT a suitable alternative for regular server-level backups that include all your assets. The backup as currently available is meant primarily to easily backup the database, and have the means to revert an upgrade should that be needed.