Hey there. Good question. You don't need to write an essay about your GMAT unless it’s really really low (we are talking about 10th percentile or lower). If you have a 670, or even 650 I wouldn’t write a whole essay about it. Plus, really, what can you write? All they will think is that “maybe you should have done better”. So instead of that, don't worry a bout your GMAT. Your score is your score. And now beat all those OTHER essays!