Hard drives lie. SMART data is not thorough and it is not trustworthy. Across dozens of drive failures over the years, I've never seen SMART predict a failure before ZFS detected data loss or the OS reported 'drive is slow'. SMART is not worth the effort to monitor.

Filesystems don't read SMART data. You might have a separate daemon which monitors SMART.

ZFS checksumming is amazing for this. You know, without doubt, which file(s) are bad. You can still use failing or unknown quality drives because the checksumming will protect you from silent data corruption.