One percent of coupons redeemed doesn't seem like a great rate, but after speaking to a number of people in the coupon business, I learned that one percent is respectable. Two percent is very good. And while no one would give me exact figures, companies do make a profit from coupon campaigns.
There's two reasons: loyal customers appreciate the coupon and continue buying the product, and new customers purchase a product they wouldn't normally have bought, like Better 'N' Eggs, (which I'm still not convinced is better than eggs), and will possibly continue to purchase the product.
In addition, coupons act as small advertisements. Someone may buy Zest soap because a few days earlier they unconsciously saw a Zest coupon while thumbing through the paper in search of the Travel Section.