It used to be important for survival. I don't think it is anymore.
Discussion
When was it important for survival?
Back when winters were hard and there wasn't enough agricultural produce to last through it.
In Arabian deserts, in ancient days, camel milk was important because it was liquid that that can be stored in udders for longer than you can find water. Basically, travellers finish their water in their containers, then start using camel milk.
Sheep milk, on the other hand, was an important source of protein. It was also used as a store of drinkable liquid.
Don't underestimate the power of milk in harsh conditions.