That depends entirely on how valuable that data is and how volatile the data is.
If it's your MP3 collection, daily backup is fine. If it's you're customer order database,
losing that after a busy day, an hour before your backup job runs would be considered
Usually the real benefit of NAS over on-server storage is scalability - it's normally cheaper
and easier to add additional disks and grow your LVM partition over new RAID arrays on a NAS
than on a server.
You can never have too many backups of important stuff though - preferably backing up using
multiple jobs or scripts to multiple places, preferably one a "push out from server" and
another "pull in from server" kind of job, to project from breakdowns in scripting and cron
When you lose connection, the company which serves offsite backup goes bankrupt or some
disaster destroys your offsite backup it is always good to have a second option
Thanks, that's helpful.