We talk endlessly about improved software quality and reduced risks, but deployable software is the most tangible asset to “outsiders”
such as clients or users. The importance of this point cannot be overstated.

You can manage scopes of time, cost, and quality much more effectively by basing your decisions on working software with actual feedback and metrics, not just task items on a project schedule.

A set of requirements is complete if and only if it describes all significant requirements of concern to the user, including requirements associated with functionality, performance, design constraints, attributes, or external interfaces.