Tow/Haul button: what is it for?

My experience on a small class C was the Ford constantly shifted gears so I talked to Brazel's RV in Washington and they educated me on Motorhome engines. Ford produces an engine and transmission which is tuned to get the best mpg in a vehicle, which will be the vehicle they sell the most of. The pickup. The pickup does not run around with much of a load so just know your class C shift points are tuned for the best fuel economy and shift points for a pickup. I bought a ECM programmer from them and installed a tune specific to the engine and transmission in the Phoenix Cruiser I had at the time and what a pleasure it was to drive from then on. No constantly changing gears at the slightest grade, it added about 50 HP and a lot more torque and the torque converter stays locked up longer to reduce heat in the transmission. If you never go up and down hills you would not see any benefit but traveling through Colorado it was a joy and the TH still works awesome going downhills. After talking to Brazel's about why all the gear changing it all made so much more sense as to the why my Motorhome acted the way it did.