Re: Backup is hard. Doesn't mean it should be ignored.
When the time came to ship the backup tape to the disaster-recovery location, no tape drive there could read tapes written by the original drive.
I have also seen this with optical media - readable (probably just) on the original drive, not on another. Probably not after several years either.
As you mention, snapshots are a brilliant idea - instant copy of a whole file system for backing up so (mostly) no inconsistencies, and with copy-on-write like ZFS you only need space for the changes so having many per day is not a high cost. However, as you mention in some cases the on-disk file is not always in a consistent state when a process is using it so having time to do a snapshot with no modifications is also good.