Business Reasons to Publish a Book

A study by RainToday.com, The Business Impact of Writing a Book, found that 94% of the authors surveyed said a book improved their brand, 95% said it generated more speaking engagements, 96% reported it boosted their number of clients, 87% said it allowed them to charge higher fees and 87% said it allowed them to generate a more desirable client base.
Sometimes, a book provides a less obvious benefit. A regional healthcare company used a corporate history I wrote as a recruitment tool. Prospective employees unfamiliar with the company received a copy of the book as a way to introduce the organization and illustrate its strong record of achievement.
Books provide their authors with credibility, more so than any other marketing medium. Think about those interviewed as expert sources by the media. Invariably, the people getting the attention are book authors. There's a saying that, if you want to get booked, you need a book.

Keep in mind, getting rich from your book is unlikely. More likely, the book will cost you money and generate profits for you in ways other than book sales. A comment from an article about ghostwriters in Inc. magazine notes: "The smart 'authors' today view their books as loss leaders." (Inc.'s italics.) This seems realistic to me.