The network effect refers to the phenomenon where the value or utility of a product or service increases as the number of users grows. It is sometimes called a "demand-side economy of scale. (Customers will demand to know where they can collect S&H Green Stamps)
This is where a coalition program really shines!
Businesses with 500 customers.
Business 1 engages their 500 customers in the program, another business joins and engages their 500 customers in the program, 10 businesses join and engage their 500 customers in the program. Now there are 6000 customers that can be engaged in the program by the businesses in the S&H Green Stamp program.