Well, typcially it is suggested and best practices that you get a backup of SQL and Storage each day. That way, just in case something bad were to happen, you've got a recent legitamate backup. It's not necessary to backup your Indexes each day as these are usually easy to recover in the event of a failure, just restore and update. For indexes, I would try to get a backup a couple times during the week. On a side note, you may want to backup your Journal indexes every day, but mailbox archives this typically isn't necessary.