In-depth coverage of subjects, overview of big topic, background information, bibliographies of additional sources. Some books need to be read as a part of foundational knowledge for particular studies. Example Kotler's Marketing Management for Business Studies and Kotter's Leading Change for Human Resources studies. The format does not matter (e-version or not).
It is better for students and other people to use books for research instead of the internet because the internet contains a lot of unreliable and questionable sources. It is better to use primary sources when doing research which come more from books and other sources, rather than the internet.
It is not necessarily hard copies of books that makes a resource reliable but the credibility of the resource. The internet now features electronic versions of many traditionally trusted resources and has even spawned some new ones. So it is not necessarily more beneficial to use books instead of the internet to conduct research.