Varghese explains a very specialised but critical field. He presupposes on your part an already extensive knowledge of TCP/IP and its routing protocols. The book usefully offers on its inside cover 15 principles for overcoming network bottlenecks. It seems fair to say that the bulk of the book is devoted to explaining and using these ideas. Undoubtedly, other books have elucidated most of these. But maybe not as explicitly and cogently as Varghese.
One key motivator mentioned in the text is to defend against network attacks. For this, it helps to be able to quickly analyse as many IP packets as possible. Perhaps an unfortunate commentary on today's Internet, inasmuch as this will be the most important reason for some of you to get this book.