I think one use would be to search for information directly from a book, rather than get a garbled/half-hallucinated version of it.

You don't need AI for that. I get the optimistic spirit of what you mean though.

Optimized information retrieval of complex text is AI.

garbled/half-hallucinated is probably what you would've gotten 8-12mo ago but now adays im sure with good prompting you can pull value from any book.