[dnanian]

The point of the Sandbox is that if you install a system update, driver or application that causes your system to become unbootable, you can simply boot back to the original drive and everything's works -- and, in addition, any work you've been doing is all up to date as well.

With a backup, your work is going to be restored along with the backup... which means you'll lose what you've done between the backup and "now".