Promotion is an excellent tool for effecting price discrimination, where people who are willing to pay more for a product are allowed to. In order to discriminate, there has to be an attribute which not all the population have. This requires a basic knowledge of the population's attributes and how they relate to other attributes.
It's also effective as a means of persuading new users to try a product (the cost of the trial is less). Since the cost is less, the overall risk of trying is lower, which tries to get around the consumer's bias: better the devil you know, than the devil you don't.
Time to go read more on effective price discrimation.