Advisory Committee as External Evaluators

I've been wondering about this. The advisory committee is given the research questions and goals. They are brought together to ask the critical questions on whether the design and process are yielding credible and practical evidence. Do they judge the worth or merit of the research design and process at all?

As an internal evaluator I act as a critical friend, asking what are we trying to find out. I think this is a characteristic of any good researcher. This is a meta-role. The person looking at what is being done, but also doing it at the same time.