If you're an editor, you learn the value of keeping the book handy. If someone quibbles about a certain red mark you've put on their work, you quietly point out that uniformity and clear style are vital to the company. End of quibble. And superbly indexed. Even saying you own the book could help you get a job.
Editors love rules.
We heard one editor interview a woman and the editor went on and on about the different ways to punctuate sentences in bullet lists. The Economist Style Guide . The book is amusing. And it tells you a lot in few words. This is the house that Jack built.