It shows people that you know what you are doing and it instills confidence in people. If you want trusted status and be an authority in your field, you will need to publish a book or how-to-guide. Even if you own a small business such as a hardware store or home design company. Publishing a book will show that you are an expert and it will directly target your field. Publishing a book is now easier than ever. There is no reason why you shouldn't publish a book. There is no better way to gain trust than publishing a book.
You are not aiming or critical acclaim or to be on the New York Times top ten best sellers list