My reason for my setup is very simple:
I favor SPEED over redundancy on my OS/Application drives. There is nothing, repeat nothing, on my OS/App drive that cannot be reinstalled in a matter of a couple of hours if those drives were lost/corrupt. They can be restored from an image in under 1 hour.
My data is invaluable and cannot be replaced. Even further, would require significant down time to restore; thus, RAID5. The RAID5 has a hot spare, and is hot-swap capable.
