This tactic helps the companies in promoting their product by giving rewards to the customer for every purchase in form of points. These points can be later redeemed for different rewards specified by the company.
Airlines use frequent flyer miles for its regular customers which you can redeem for a free air ticket
Banks award points on credit card purchase which can be used to get different goodies
A similar initiative was launched by Bharat Petroleum few years back in the form of Petrocard