If you're serious about data backup, and/or you use one of Zyxel's 4-bay Personal Storage solution (the NAS540), a RAID storage system provides a dynamic way to preserve your priceless data. But how does it work?
Simply put, RAID stands for Redundant Array of Independent Disks and how it works is by combining multiple physical disk drive components into one or more logical units for the purposes of data redundancy, performance improvement, or both. It's particularly useful because if you happen to have a drive fail, your data is backed up on a combination of the remaining drives. For example, the Zyxel NAS540 can protect your personal data from hard disk failures. In case any one of the disks failed, you can still access your data safely and restore the normal RAID protection with the failed disk replaced.
The simple answer to the question in the title is, a RAID data system is critical for those who store sensitive/irreplaceable data on hard drives. Film and photo professionals come to mind, particularly because they are not only working with irreplaceable data file types, they're also large in size which makes them difficult to store in online databases. That's yet another reason a personal cloud solution makes sense.
(If you want to learn more specifics about how various RAID types work, check out this fantastic summary here: https://www.prepressure.com/library/technology/raid)