If the reader doesn't understand the book or report, that isn't going to happen. If the writing is hard to follow, ambiguous and confusing, it may have the opposite effect to that intended. Savings Clear, appropriate writing can save everyone's time. It will save your time, because your readers won't need to come back to you to check points that are unclear or inadequately explained. If your writing is intended to prompt an action, you need to be absolutely certain that readers understand exactly what you are suggesting.
Ambiguous writing can be, and has been, the cause of expensive litigation.
Books and reports must be 'user friendly' so that information can be rapidly accessed and understood. Professional technical writers make good books and reports. Like designing a product or managing a business, writing a book or report requires specialist skills. Some people think that the expert on the subject of the book or report would be the best person to write the final text. But experts on topics are sometimes the least able to explain them, because they find it hard to put themselves in the position of people who know nothing about the subject.