What is the thought behind boiling the sweet potatoes in milk? Any downside to plain h2o?

I think that cooking the sweet potato in milk just adds another layer of creaminess and normally when you make mashed potato either sweet or otherwise you add heated milk or crean. I make mashed sweet potato with either sour cream or creme fraiche frequently and I don't boil the potato I bake them wrapped in aluminum foil until they are very soft, then I mash with the butter, creme fraiche etc....Any way you do it its a wonderful creamy treat. I love the recipe Merrill posted it sounds yummy!