If you write to your audience your text/media will be more successful, effective, efficient, and usable. Audience is the most important of the three parts of the rhetorical situation. If you do not fully consider and write or design for the audience, it doesn’t matter your purpose, context, or anything else. You were unsuccessful. If they can’t read it, don’t get it, or don’t care, your purpose has not been met, and context does not matter. So, whenever you are writing or designing media you need to think about who you are writing or designing for. Be as specific as possible, because the more specific you are the more you will be able to write to that audience.
To find out more: Screen Space 21: The Rhetorical Situation Part 1—Audience