Helpful yes, but far from enough. It only helps in some scenarios (like accidental deletes, malware), but not in many others (filesystem corruption, multiple disks dying at once due to e.g. lightning, a bad PSU or a fire).
Offsite backup is a must for data you want to keep.
Always use /dev/disk/* (I use by-id) for RAID, as those links will stay constant even if a disk is renamed (for example, from sdb to sdd).