You read something and read it again, go back and reread it, you have some trouble understanding it, or maybe you have some thoughts you want to pursue.
A smart reader (browser extension, e-book function, etc.) that suggests more information based on your behavior while reading. For instance, if you read at a certain pace, and you stay longer on a paragraph, you might get a pop up asking if you need to dig deeper into details or would like to expand by getting related information.
You don’t have or want to spend the time to read the whole book.
Publish a slideshow for popular books that include the main points expressed in graphs, charts, short bullet points, etc. You go through the slide show, maybe with an expanded narration explaining it in a short time.