NEW YORK ( MainStreet) -- There are some people who just can't get enough of franchising, so much so that not only do they own multiple franchises of the same brand, but they have created or invested in more than one name. Franchises are attractive businesses to operate if you want to own your own business but don't want the hassle of starting something from scratch. From a franchisor's standpoint, it can be very profitable if the product or service answers a need in the marketplace and there is an operations model behind the product or service that is efficient and easily replicable. Sales by franchises total more than one-third of the U.S. retail market, and more than 7 million people are employed by a franchise, according to the International Franchise Association. "One of the reasons that many franchises have been so successful is that, in franchising, a business synergy is created. Franchisees brought together under one trademark can achieve things that as individual business people they could not do. Group advertising, buying power and the sharing of ideas are some examples of what can happen," the IFA says on its Web site. We found five franchisors or franchisees who made a career out of either creating successful concepts or investing in multiple proven brand-name companies. Here's what they had to say about serial franchising.