Any sale is a good thing, of course. But a sale from a physical store can be a better, because it carries ancillary benefits, or at the very least forestalls the ordering system from just deciding to not even carry an author's books anymore. This is why, even if a book you're looking for isn't on the shelf in the store, I recommend asking if they can order it in for you, instead of getting it from Amazon. Sure, go online for the really arcane, hard-to-find stuff that the store can't order, but if possible, get it from a physical bookstore.