I thought you were asking for a good reason(s) to have one... When you asked did you already know there wouldn't/couldn't be any reason good enough for you?
I'm just advising if there is a way to eliminate a leak source, a malfunction-able item, then it's a good idea. Lot's of ways to pinch off a hose on the hiway, if you really needed to, but that would require you to have whatever part you are replacing with you also. If it's a necessary part on a gravity feed system, OK.
