Since this is a Class C motorhome forum, the OP is probably referring to driving a Ford E450 based 2012 RV. If so, it will have a TorqShift automatic computer controlled transmission in it with it's push button controlled Tow/Haul mode.
For the potentially dangerous situation of descending hills in a 11,000 lb to 14,500 lb. Class C E450 based RV, the Tow/Haul mode in these motorhome transmissions works splendidly. When going down hills, there is no need to have one's attention diverted to reaching for gear shift levers/pads/buttons once, or more times, while going down a grade. In fact, there isn't even any need for turning Tow/Haul mode "ON" at all in these modern Ford E450 transmissions whenever going down hills - just leave the transmission "IN" Tow/Haul mode all the time. This then gives you BOTH engine braking when slowing down in normal driving plus .... engine braking when going down hills. It's all automatic so you can keep your eye and concentration on the road at all times - while reducing repair costs for brake pad replacement.
I've driven standard transmission vehicles for many years - including trucks with the long manual shift floor lever and high performance sports cars with flick-of-the-wrist short manual shift levers - and believe me, it's a distraction to have to pay attention to what gear you should, or shouldn't, be in.
Automatic transmissions make driving safer and treat engines and their drive trains better.