It's not quite pointless. A prepared outline/mind-map gives you a roadmap for learning beforehand; it can function like a good index.

It's better to memorize domain knowledge upon paths that are clearly understood (thus you are memorizing well-worn, acceptable paths), rather than synthesizing your understanding of a topic as you go along. The second is prone to mistakes and mistaken understanding, unless you're a subject matter expert or charting new domains of knowledge.