RAID is only useful if you need to ride through a hard drive outage with no downtime. That's redundancy. Another form of redundancy I often practice is a whole mirrored machine ready to take over. Or it can even be live all the time for certain protocols like DNS and NTP servers.
We can live through the inconvenience of a few hours or even days downtime if a drive or machine fails. But the backups (plural emphasis) are important.
