RE: Butter-the essence of cooking
My understanding is that salt extends the shelf life of butter as well as (potentially) masking off flavors. Unsalted butter is always preferred for baking because (as somebody famous said, "Cooking is art. Baking is science.") the use of salted butter would add an unpredictable variable.
We switch back and forth between the two depending on what we like: for instance, I always like salted butter on toast.
I don't know if this is the proper way to go about it, but if I need clarified butter, I simply melt a bit more than the recipe calls for, let it stand a while so the water & milk solids settle out, then chill it. When it's firmly set, I simply remove it from whatever it was in and remove the unwanted stuff.