It's handy. I've done some 60m/70m double rope raps, and having the extra 10m meant getting to the ground rather than downclimbing. Not necessary perhaps, but really handy. Helpful if you can't downclimb because there's a party on the only good line.
Easy to use the rope as an anchor, can anchor into things far back from the edge.
If an end gets damaged you can cut off up to 30' and still have a usable rope.