Scenario

At the beginning of a project it is not always possible to define in great detail all of the requirements, work elements, and deliverables that will be involvedespecially when a project is scheduled to last for a long time or involves several phases. In such cases, details can be progressively elaborated as the project evolves. As these details are established and addressed; however, the scope of the project may seem greater than originally anticipated and revisions may be necessary.

Question

How should a project manager or team go about managing changes to the Project Scope Document and what are the points and pitfalls that should be kept in mind?