A coupon achieves something a price cut cannot: it gives a discount to some buyers while leaving others paying full price for the identical item.

Effort is the sorting device

Obtaining and applying a code takes time and attention. Shoppers differ in how much that effort costs them relative to the money it saves.

Those with more time than money will complete the steps. Those with the reverse balance will not, and will pay the standard price for the same goods.

The seller does not need to know which group any individual belongs to. The coupon sorts them by their own decision, which is what makes the mechanism practical.

Two prices from one shelf price

Without a coupon, a seller must choose a single price and accept either lost volume from price-sensitive buyers or lost margin from those who would have paid more.

Splitting the market removes that trade-off. The list price captures the less sensitive group and the coupon captures the rest.

This works only where the two groups cannot easily trade with each other, which is why coupons are restricted to one use, one account, or one transaction.

Friction is deliberate, not accidental

Requirements to register, to enter a code, to hold a card or to redeem within a window are not clumsiness. They are what stops everyone from taking the lower price.

Reduce the friction too far and the coupon becomes a general price cut with extra steps, giving away margin to buyers who would have paid full price.

Increase it too far and the price-sensitive group abandons the process, which costs the volume the mechanism was designed to capture.

Coupons carry measurement with them

A code identifies where a shopper came from, which campaign reached them, and what they bought, none of which a shelf price reduction reveals.

That attribution is valuable independent of the discount, and some codes exist mainly to measure a channel rather than to move volume.

It also makes the cost of the promotion precisely countable, since only redeemed codes cost anything and every redemption is recorded.

Reversibility is the underrated benefit

A published price reduction is hard to undo, because raising a price back is visible and reads as an increase to anyone watching.

A coupon expires on its own terms with no announcement, and the list price never moved, so the reference point survives the promotion intact.

This is why coupons proliferate in categories where price positioning matters and why sellers who compete on stable low prices tend to use them least.