Everybody likes to get a discount, and everybody likes to feel special – which is precisely what makes coupons one of the most powerful marketing techniques. With coupons you gain the ability to create customised, yet mass, discounting options. Simultaneously making people feel unique & special, whilst attracting them in large groups. There are plenty of companies that do this exceedingly effectively, GoDaddy being the one I’m most familiar with (you can find GoDaddy coupons almost everywhere).
So you can get a discount if you belong to Group ABC, made a previous purchase of product XYZ, or happen to know a friend who has a referral coupon!
Another frequently overlooked advantage is that let’s you sell at a lower price without making your product look cheap, because the Retail Price is still high.