According to my Dad, who's full timed for 6 or 7 years, you should always carry a spare. If a hose gets a leak or a connection piece breaks/fails, it's good to have back-up.
I use a 15' Rhino, the spare is about 12' (because I modified it to fit the allowable storage space), but I've never used the spare nor needed it as an extension. However, we have a truck camper with dump valves that are very accessible and positioning the rig close to the dump inlet is easy. Also, we've only had the rig about 14 months and have only visited 25, give or take, camp grounds.