As an academic, I have to read a lot. A former professor of mine, Klaus Dicke, underlined the importance of writing excerpts of articles and books, one's reading: After you read an article or book, you want to quote from (directly or indirectly), you write down the essential ideas and quotes of the publication. While doing this, you keep also track of the page numbers, the idea or quote can be found. So, the ideas stick better to your head and you can find these faster than just by highlighting in the text. An excerpt done by hand might look like this example from the beautiful blog "Minimalismus und mehr".

Handwritten excerpt, seen on the blog MinimalismusUndMehr