Yeah, Apache has thorough documentation at apache.org, and yeah, after 6 or 7 years I've learned a lot by reading through Apache's conf files. But this book does a few things extremely well to make configuration much easier, quicker, and better.
There's good examples - you expect that with a name like "cookbook". But each example is backed-up with excellent explanations and references. The particular problems I've wanted to solve haven't matched the book's examples, but they've been close enough to adapt the solutions to what I've needed.
I've also appreciated how much this book has helped me how to *think* in Apache. Its use of examples and explanations helps to paint a top-down view of Apache, and help me analyze problems methodically instead of hunt-and-peck through a flock of random configuration parameters.
A nice combination of technical know-how, tuturial, and clear writing makes this a darned useful book for me.