A good scope statement does more than describe what a project will do or produce. The best scope statements will also describe what is not to be part of the project. In other words, the scope statement builds a fence around the project that contains the project deliverables and only the project deliverables.
This fence provides the first line of defense against scope creep. In effect, a strong scope statement that also describes what is not to be included in the project, provides the project manager with the strongest tool to manage creeping scope expectations. Together with a robust change management system, the project manager has the tools to corral expanding projects.