Different price at different quantities, without a mental calculation.
Sell one at retail and a dozen at wholesale from the same product record. Slabs apply automatically as the quantity changes, so the cashier never works out which rate applies and a wholesale customer is never charged retail by accident.
Who it is for: Kirana, wholesale, and anyone selling the same item in singles and cases.
Why it is included: Quantity pricing — a lower rate above a quantity you set, worked out at the counter instead of in the cashier's head. Included with the till rather than sold on, so the price a shop quotes for a dozen is never a manual calculation.
Included in the till. The base price covers it, so there is nothing extra to buy.