Another consideration might be, in the event of double or triple headed locomotives, or helpers cut in throughout the train, unless all the locomotives had an aux water bottle, the distance between water stops was only as long as the locomotive with the smallest water supply.

Multiple spots for filling all tenders and water bottles would be tricky and time consuming. It would seem that aux tenders worked best for trains with one locomotive, and in places that could utilize wyes, as opposed to turntables for turning the locomotives.