One primary benefit of sizing with testable requirements is communicating the system size to management, developers, testing staff and end users. Often, missed deadlines, cost overruns and other project management problems are due to underestimating the scope, and possibly, the complexity of the system being developed.
To ensure an understanding of what is being sized, the software estimator must understand the scope of the system and clarify the system limits. The use of the Requirements Sizing Matrix helps take the mystery out of the estimates.