HelpMeRick.com is not a geek website so I'm not even going to get into what RAID [1] is other than it is something geeks do to their computers.
However, I will say that I have had a number of clients over the years who have had a friend, relative or computer salesman talk them into going with a RAID setup and it has turned out to be a giant problem.
Often RAID is installed as a "backup" system. Essentially this type of RAID setup uses two hard drives. Whatever happens on the first hard drive is automatically duplicated on the second hard drive.
This means if you experience a major Windows or program error, such as a deleted file, the mistake is automatically duplicated on the second hard drive. That's not a good backup system.
There are many more problems you can experience with a RAID setup. In fact, it takes a huge computer geek to setup, maintain and troubleshoot a RAID setup.
Please, if you are one of these geeks, do not setup a RAID configuration on your parent, grand parent or friend's computer unless you plan on being able to be physically present if problems occure.
I found this great article [2] written by a real computer geek explaining why RAID is almost always a bad idea.
Links:
[1] http://www.webopedia.com/TERM/R/RAID.html
[2] http://www.pugetsystems.com/articles.php?id=29
[3] https://www.paypal.com/cgi-bin/webscr?cmd=_xclick&business=rick@yourpcpartner.com&item_name=Buy
[4] http://www.yourpcpartner.com/node/1329
[5] http://www.yourpcpartner.com/node/673