Today, more and more businesses are migrating their products from a purchase-based to a subscription-based model. Ever since Salesforce.com pioneered software as a service (SaaS), companies across industry sectors—B2B and B2C alike—have made the move. In the entertainment business, Netflix ushered in monthly-DVD and online-streaming subscriptions, and Spotify supplanted iTunes. Even the everyday razor has been transformed from a one-shot transaction to a monthly plan, with Dollar Shave Club. We...