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.