Well, my opinion is that books are read for a more thorough study and the Internet is used for an overall view of the subject. It so happened that I have already explored this subject when working with the guys from https://ihatewriting.net/the-best-personal-statement-writing-service/. From what I read and understood, books are indeed more reliable than the sources on the Internet because they have been reviewed before publishing. Though of course, it is much faster to find the needed information online.