I have used it in the past but not for a long time as if I ever I need it, it is only for baking and only need a small amount.
I HAVE however discovered powdered coconut milk which is great as my daughter in law cannot drink dairy, and I can substitute this for many recipes just using less if it is a savoury one.
So, NO, I do not use powdered ordinary milk, though can see it would be handy when say, travelling in a caravan or similar!