Impact and portfolio answer different questions. The first is about the change the organization creates. The second is about how it recognizes, develops and manages its institutional possibilities.
An organization can have an extraordinary program — recognized and well documented — and still remain exposed because almost all of its institutional value depends on that single front.
Separating impact from portfolio makes it possible to tell strategic focus apart from unintended dependence. The problem isn't having few projects. The problem is not knowing whether that concentration is a protected choice or the result of being unable to develop other possibilities consistent with the mission.