Answering number 4 is truly optional. It is up to you to decide if there is something else that is important which you would like to share that you did not feel came through in the rest of the application materials. The regular MBA essay is subject to some more stringent guidelines and is intended for more explanatory purposes. The MBA for Executives optional essay prompt is more open of a solicitation, in my opinion.
I certainly wouldn't write an essay just for the sake of writing an essay. Complete it only if you feel it is necessary.