We all (hopefully) backup our PBX's - our config files, databases, even system audio and logs, some of this can be backed up hourly, daily, or weekly, so in all likelihood, you will have at least two backup processes probably more, but where do you back them up to?
Local storage? It's fair to say nearly everyone uses this, but is that the only place you have them? What if your disks fail? A lot of good those backups are now you can't access them!