Usually studying a test book is reconceptualizing it in whatever way fits the way you learn. For some people that's notes, for some it's flash cards, for some it's reading the textbook twice and they just get it.

To imagine LLMs have no use case here seems dishonest. If I don't understand a particularly hard part of the subject matter and the textbook doesn't expand on it enough you can tell the LLM to break it down further with sources. I know this works because I've been doing it with Google (slowly, very slowly) for decades. Now it's just way more convenient to get to the ideas you want to learn about and expand them as far as you want to go.

My issue with using LLMs for this use case is that they can be wrong, and when they are, I'm doing the research myself anyway.