The code on the coupon helps the cashier to directly scan the coupon along with the billing of the product. Thus saving a lot of time at the cashier's desk.
The usage of the coupon also gets registered alongside the discount and the procurement price of the product against which the coupon is used.
The cashier needs to only check physically if the coupon is torn or dilapidated. Otherwise, the validity of the coupon can be known the second cashiers.