You want to study the conceptual structure of something, to gain a better understanding or to acquire the jargon of a topic. Business analysts do it when starting on a new assignment. In a new environment with new people, unknown habits and a lot of catching up to do, they pick some documentation, courseware, legislature or other jargon-laden documentation and make an Ampersand model. Making sense of piles of new material goes much faster if you try to make an Ampersand model on the side.