Many book critics use a variation on this method. In the pre-digital era Michael Dirda, the Pulitzer-winning critic for the Washington Post, said he had filled many volumes of those "blue books" once used for college exams with his notes on books.

Instead of summarizing passages, I jot down modified bullet points that highlight aspects of books that critics look for: e.g., "Theme: [followed by a line or two about what the theme appears to be and a supporting quote]" or "Point of view" [ditto]. It's vastly more helpful than just highlighting passages. If you do this, by the time you start writing a review, you've already thought about the theme of a book and have notes like: "Shift from protagonist's first-person POV to omniscient narration."