Not that big of a deal when it is a backup. Raid is not a backup solution, it is a 24/7 uptime solution. If the main drive dies with JBOD, then you have the backup. If a backup drive fails, then you still have the main. Trick is to ensure any drive issues are dealt with immediately and no backup runs if there is a smart error or similar on any drive.
So having software that monitors drive health and email/notifies you is necessary.
Secondary benefit of JBOD is all drives in a pool are still readable separately.