The companies like McKinsey is called consulting firms the major work that is done by these companies is to consult other companies so as to help them how to solve big problems in their business.
The question can range from should they enter into a particular market or not, what they can do to scale up their product, etc.
Consultant are very expensive to hire so it is adviced if the answer really matters for you then it is good to hier one else it is not.