People do not know where to start reading. They are look for magic place from which they should start and keep reading. Place where they can return and start again. Second: link for example to other parts of text and docs are extremely disturbing. Why? Because you have to make a decision of continuing reading or reading the text in the link. Show them the path and let them keep going on it. And last: People cannot work with text which they are reading on-line. There is not easy possibility to highlight text with different colors, write notes and mainly let them to form the text on their own way. You can do this with printed book on paper.. A lot of small places for books, articles, man pages, web pages and own notes.. If you have the possibility to take care of text you are reading, than the text is part of your live and the content is valuable for you, because there is print of your reading, print of your effort which you do not want to lose.