<p>If you feel like your application doesn't give a good enough window into your personality and who you are as a person, you should write it. But you mentioned you're a bad writer, but I would suggest writing it, just get lots of feedback for it and edit it accordingly. But if you're got a pretty good app and you think the adcom would see you thru your app, i guess you're okay without it.</p>
<p>optional essays usually either hurt you or help you. if you write one bad, of course it'll hurt you, but if you write an amazing one, it might be the thing that tilts in favor of your admission</p>