Typically three. Two local, one remote. Consider not RAID protecting the local backup.

Not everyone has that kind of cash lying around, especially if the pool is large and the data is not critical.

You need to do more than just keep a backup of current state, if you want to deal with problems other than complete failure/destruction of the primary. What about accidental deletion and incorrect editing (done too long ago for "undo" to work)?

>What about accidental deletion and incorrect editing (done too long ago for "undo" to work)?

Eh? We're talking ZFS here. Built-in atomic low cost snapshots are part of the core feature set. If we're talking using a pool and backing up another pool it's a reasonable baseline assumption that one would be using either their own or one of the many mature scripts to have regular automatic snapshots and retention schedule. Ie., once every 10 min for a day, once an hour for a week or two, once a week for a year, and monthly thereafter (or whatever fits your use case), along with preservation of any manual custom snapshots. I mean, it's right there, for free.

Fair point, but the comment I replied to did not mention configuring anything like that, and while it is all there for the taking it isn't automatically configured.