Ray Kroc lost money on franchising burger sales; somebody advised him that the real money is on the real estate - choosing sites, leasing the same to the franchisee and thus can make money the moment a lease contract was signed.
So if there are multiproduct offering, you can a price leader (loss product) so that you can entice the customers buy the more expensive product.
Or have a free product (a bait so that the profitable product can be sold bought)
