[Borgbackup] Rationale for keeping a copy of the repo key

[Jonas Olson]

It is recommended [0] that one stores a copy of the encrypted repo key 
in a safe place. Naively, this would seem unnecessary, as it is stored 
in the repository and no copy is normally needed. Is the reasoning that, 
in case of filesystem corruption, you still have some chance of saving 
parts of the backup as long as the key is safe? The documentation 
doesn't spell it out, as far as I have been able to see, and I'd like to 
make sure I understand it correctly.

Regards,
Jonas Olson

[0] "Make a backup copy of the key file (keyfile mode) or repo config 
file (repokey mode) and keep it at a safe place, so you still have the 
key in case it gets corrupted or lost. Also keep the passphrase at a 
safe place. The backup that is encrypted with that key won’t help you 
with that, of course." 
<https://borgbackup.readthedocs.io/en/stable/usage/init.html>