Hard disks have been known to crash 😀 Someday you may need to remove those files from your raid.Im just sharing with you the work flow that most all professional editors do. Its totally your choice whether to do it or not.
You want a master since its a lot faster to make an h.264 from your master then from your time line in most case. If your drives or system dies you could still get your client a copy. Your situation may vary enough from my experience in video production facilities to warrant not making a master, but I think its a very unwise thing to do.
Tom Daigon
Avid DS / PrP / After Effects Editor
http://www.hdshotsandcuts.com
Mac Pro 3,1
8 core
10.6.8
Nvidia Quadro 4000
24 gigs ram
Maxx Digital / Areca 8tb. raid
Kona 3