What if you are writing not for yourself but to reach someone else? It might be that you hope to reach a single individual which can be done in a letter to a friend, parent, or child. You might be composing an anecdote or speech for a small or large group, or you could be creating an industrial film, designing a text book, or fashioning a timeless work for all humanity.
In each case, the scope of your audience becomes more varied as its size increases. The opportunity to tailor your efforts to target your audience becomes less practical, and the symbols used to communicate your thoughts and feelings become more universal and simultaneously less specific.
The audience can thus range from writing for yourself to writing for the world. In addition, an author’s labors are often geared toward a multiplicity of audiences, including both himself and others as well. Knowing one’s intended audience is essential to determining form and format. It allows one to select a medium and embrace the kind of communication that is most appropriate — perhaps even a story.
From the Dramatica Theory Book