According to RainToday.com writing a business book can greatly increase your image, client base and ability to charge higher fees.
From my experience writing a book makes a big difference in how people respond. I have been hesitant to say I have written, or pull out a copy of my marketing books because I feel like I am being cocky. But the reactions I get are very positive, usually people want me to sign it and are very grateful. Of course I have picked up a few consulting gigs from the book as people are very impressed with my knowledge. The funny thing is, most of them never read the book, they just assume I'm smart since I wrote it.
One of the things I recommend to my new clients is to write a book, or at least or short pamphlet sharing their knowledge of the industry with customers. It positions you as an authority in your field and provides a nice chunk of useful information for current and potential clients.