Clear, appropriate writing can save everyone's time. It saves the writer's time, because the readers don't need to come back to check points that are unclear or inadequately explained. It costs money to write - and it costs even more to do it badly. Let's look at the possible cost of a two page letter.
Many people still write their text out long-hand and give it to administration to type and tidy.
The letter goes to its readers, and the dollars really start to mount up. I know you think you know what I said, but I wonder if you know that what you think I said is not what I meant. That describes a lot of modern business writing. They can act on what they think it meant. They can ring the writer and ask for more information.