Snapshots (as opposed to backup) are not meant to be used regularly as the proffered method for recovery.
The outcome is very big (entire root partition + some of /var/log partition and some extra) and this is the main reason for this feature not having the option for scheduled operation (as in Backup).
Its main purpose is to be used after a major configuration change such as completing gateway or management server first time configuration (including HFs, routes, etc.) and after installing a Jumbo for example.
Snapshot will restore everything from scratch and takes time.
Backup is the preferred method for restoring the GW/MGMT/Other state of software level (policy rules, IPS files etc.)
I hope this sheds some light on the subject and you find it helpful.
Anyways the Gaia admin guide will be updates soon to address this knowledge gap.