Most businesses pay for services like advertising in advance. They design an ad and pay a newspaper, magazine, billboard or web site to display it. The display must be paid for whether or not the ad brings in any customers. Profit sharing plans, on the other hand, reduce the up-front cost to advertisers. Web site owners sign up to display the ad but only make money when site visitors do whatever task is defined in the profit sharing agreement. The agreement might specify that payments will be made for click-throughs, registration (leads), or sales.