........... 1. Towing Heavy Loads
If you are pulling a large boat or you have a truck and the flatbed is loaded down with heavy equipment or supplies, you could damage your transmission if you don’t drive in “low gear.” This is because your transmission is programmed to operate and shift under the manufactured weight of the vehicle. When you significantly change the weight, it can have adverse effects on the transmission. Using low gear to tow heavy loads ensures that the entire transmission keeps the engine running at higher RPMs in order to handle that heavier load.
2. Steep Inclines & Declines
Another reason that drivers of automatic vehicles may choose to shift manually to low gear is during times of driving on steep hills or mountains. Shifting your engine manually to low gear while driving up a steep hill can help give your car a little more power, or engine torque, to make the climb without stressing the engine. Conversely, driving in low gear as you descend a steep hill can help you stay slow and steady without riding your brake or burning up your transmission. ................
https://parksidemotors.ca/when-to-use-l ... automatic/