Working software is the primary measure of progress.
– Agile Principle #7
Agile Principle 7 offers a simple guideline: true customer value means delivering working products*. This principle is important because it:
Quickly demonstrates quality. Working product means just that: a product that is developed, tested and demonstrated as working. On agile projects, you know right away how well your product works, because you develop, test and demonstrate in every iteration.
Allows immediate feedback and improvement. Delivering working products every few weeks allows you to get immediate feedback from customers and other stakeholders. For some companies, this might mean releasing a beta product to a select group of end users. Take, for example, Google's Project Glass Explorer Program. Google is releasing working versions of its Google Glass augmented-reality device to a select group of customers. Those customers will test the device and provide feedback about how they really use the product. Google plans on delivering monthly updates based on customer input.
Serves as a litmus test for project progress: On agile projects, delivery of working products changes the idea of percent complete. Because you deliver working products with every iteration, a project that is 75% complete has 75% of its features completely working. If a project must stop partway through, project sponsors still have value.
*The principle reads "working software," but as more diverse organizations adopt agile practices, the term "working products" is becoming more relevant.