Is it worth reading books on this subject?
In freediving as in many other sports, theory and practical go hand in hand. If you want to become proficient or expert, it is important to keep advancing your knowledge in the sport. For example, a training drill or a different approach taken from a book can increase performances, sometimes dramatically. The broader the freedivers knowledge the more he can call upon to assist his training.
What books should I read?
More and more books on freediving and freediving training are becoming available. Check reviews. There is however, one book that has the basics and is spoken highly of throughout the world of freediving. This is the Manual of Freediving by Umberto Pelizzari and Stefano Tovaglieri. This is a very thorough coverage of the subject and has been updated with more recent advances in the sport, in the second edition.