They're primarily used in as an ingredient. Often they are suspended in a sweet syrup and are thoroughly mashed to make a pie filling, it's actually not bad.
They’re quicker for making sweet potato pie since they’re already cooked. You add plenty of other ingredients to the filling so there’s less difference in the final product between canned and fresh
That still doesn't make sense, if you're making a fresh pie but using canned ingredients, you might as well buy a pie. I'm sure they taste OK, but sweet potato's are on of the easiest things to cook, if you want them soft before you put them in the pie, put them in a microwave for a bit.