RAID stands for Redundant Array of Independent Disks. Basically, for people that work with servers, it's uber great because it actively backs up new data on the fly.
RAID IS NOT A BACKUP, NOT A BACKUP, NOT A BACKUP. It doesn't replace a BACKUP.
It provides fault tolerance (except for RAID0). It gives you the ability to suffer a hard drive failure and keep the machine running. It should NEVER be confused with a backup. For example, if you have a RAID1 mirror and you select a folder and shift delete it, it's gone from both drives instantly. Where's the backup????
RAID 0 is generally most used for gaming and hard core machines, but has the risk of losing a MUCHO amount of data if one of the drives fails.
RAID 0 is the only version that offers no redundancy. RAID0 is a stripe. 2 drives act as one. A little gets written to the first disk and a little gets written to the second disk. If either fails, you lose absolutely everything. So, you actually have a greater risk of failure with RAID0 as you have 2 drives which could potentially fail.
Gamers believe it offers great performance because it increases benchmark scores. But for game play and such, this doesn't help your gaming performance. If you were doing video editing and huge file copies all day long, this is where a RAID0 stripe could really help you out.
If you truly want performance as a gamer, get an SSD drive. They too offer high sequential read speeds like RAID, but offer extremely low random access times and this is where the biggest bang for the buck is. Or get a drive like a Western Digital Velociraptor with higher spindle speeds (10,000RPM), but I would NOT ever suggest a RAID0 configuration to any gamer.