Books are for use
Every person his or her book
Whether we say person or reader here might not matter, but part of Ranganathan's philosophy prompts us to see our readers as individual human beings with their own interests and needs. Our obligation is to treat and think of our readers with respect and as having the right to come to us for the book or books that will suit their needs. We should also look to providing broad access and the amenities that would welcome readers to come and use their books.
Every book its reader
This is mainly a maxim for collection management. Why should we keep any one book? Because of its evident usefulness to one or more readers. This also gives direction to how we build and design indexes, search engines and results lists. The challenge with internet resources becomes how to bring forward the most likely useful books and to push the others to the third and fourth pages of results.
Save the time of the reader
This is quite simply a matter of convenience and quality customer service. Any task that can be made easier should be easy. This will give the reader time and energy to devote to tasks that have to be hard, like learning how to read scholarly articles.