This is a technical book about network and web technologies. It's not something you can apply as a skill but rather use it as a foundational knowledge in your work. Do you have to know it? No. Will it make you a better developer? Definitely.
Reading this book made me appreciate web technologies: how successful they are and how well they are designed. I feel very fortunate to have my career in web.
The book was published in 2013, and is still relevant. However it would be great to update it to 2024 since many of the technologies are much more adopted 11 years later.