Content (to backup) is King in this decision. How sensitive are your files most easily accessible (which would not be things like Keychain passwords locked up with their own password)? The more sensitive or secret the files, the more layers of protection one should generally desire.
- Should I encrypt my TM and get a fireproof drive for it? Yes
- Should I encrypt, in fireproof drive and secure it to the wall to make it hard to steal? Yes.
- Should I encrypt, in fireproof drive, secure it HIGH on the wall in a flood proof enclosure? Yes.
- Etc.
Your current decision is a simple toggle choice in software. Those others might matter too but add cost and some time/trouble to get in place. To each his own.
That shared though, along with making this easy choice, I strongly encourage the more important one too: set up at least
TWO TM backups and store one offsite... to
regularly swap with the onsite one. Just one backup drive reasonably up to date stored AWAY from the main system and current backup will dramatically increase the potential of recovery after very real fire/flood/theft scenarios.
The easiest loss after hardware failure is losing both Mac + TM due to one of those events. They are typically stored right together. If you lose one, you will likely lose the other too. However, one recently swapped backup offsite means you have near 100% recovery in
any of those scenarios.
I store mine in a bank safe deposit box for less than the cost of 2 Apple Handkerchiefs per year. For me, timing to rotate them is monthly. Worst case scenario for me is a catastrophic loss of all backup copies at the main location on the 29th day of the month... when that "last resort" backup drive would not have the freshest of new files created/added in the last 29 days. Someone else wanting to do this might choose "every 15 days" or weekly instead... or use some cloud space for the 29 days to then purge each time the next rotation occurs.
All this takes is paying the relatively low price for one more drive and then a little personal discipline to keep up with the rotation schedule. Just do it!