That's related to the broad picture in which a single API call has its proper role and place. In turn, the broad picture is made up of the business scenarios that the API call supports. It's often not easy to get the link between a detailed API call and its business context.

Nevertheless, that link is crucial when it comes to choosing which API to use, before starting to understand how the API works.

Then, I'd say that a great documentation also delivers all that.