Perhaps writing a book, screenplay, novel is more for the benefit of the author. Perhaps the act of writing it is to help the writer work through his issues or to gain insight or to leave a legacy. Some novels, books or plays may never see the light of day, having an audience of maybe his immediate family.
But then again, we do not know that until is written.
In counterpoint, the opposite may also be true. The Diary of Anne Frank, was a personal diary not meant to have an audience at all, yet it touched thousands or even millions of people.