RAID is an availability play. Backups of data that you consider at all valuable (family photos, financial records, etc) should be on write once data or offline. Many of the posts here refer to issues around physical drive failure, but its important to consider data corruption (intentional or unintentional)
All of these data replication suggestions are, like RAID, availability plays. You need to have static point in time snaps or copies; or deltas from which you can recreate points in time; to be able to recover from a data disaster. Its great that you are using rsync to replicate your kids first birthday photos to a box somewhere else, but if that folder gets corrupted you are now replicating that corruption. You are now the proud owner of two sets of useless data and the endless crying from the spouse that inevitably accompanies such.