ID Sketching's fun "Five Levels of Sketching" article reminds us that
When all is said and done, regardless of how flashy the sketch may be or how killer it may look, the essence of why we sketch ideas as designers is seeded in effectively communicating those ideas to our clients. Sketching is our language of communication.
Author Spencer Nugent goes on to distinguish between Doodles, Thinking Sketches, Technical Sketches, Presentation Sketches, and the money-shot Emotive Sketches. Check it out here.