Discounts. Allow a store owner to specify maximum product quantity which could be discounted. For example, you can have two products (the same) in the cart but only one of them will be discounted. It can be used for scenarios like "buy 2 get 1 free".
I don't see how one can set up "buy 2 get 1 free" with just "Maximum discounted quantity" field. The idea of "buy n get 1 free" is that you must buy n, and then you get another one for free. The effect I get with the max set to 1 is really "buy 1 or more, 1 is free", and thus if you buy just 1, that 1 is free (i.e. total cost = $0)
(Also, BOGOs are meant to apply multiple times - i.e. for each quantity 1 I buy, I get 1 free - thus, if you buy 2 you get 2 free)
