No. I have never needed to, unless there is a milk strike coming up that I don't know about??? We have excellent quality milk in this country, and as far as I know, no threat to the quantity available. Maybe people with certain medical conditions may use it.
I sometimes use powdered milk in cooking. I sometimes add a bit when making icing for a cake. The powdered milk adds a creamy flavour. However I don't always have some on hand as I can manage quite well without it.
I sometimes used powdered milk when we ran out of fresh milk but that was many years ago, before long life milk. I only ever use Devondale long life milk as we aren't milk drinkers as the taste is nicer and not watered down. As I bake a lot I only buy the milk when it's on special and buy 6 x 2 lire cartons at a time. I do have powdered coconut milk on hand for cooking as well.