Our clients frequently ask, “If I write the optional essay about my [low GMAT score, low GPA, bad semester in college, long stretch of unemployment, etc.], will it call attention to that weakness and overemphasize it?” In short, no. Writing the optional essay about a weakness will instead allow you to control the narrative about that issue and thereby better mitigate any negative effects it might have.
The admissions committee very likely will take note of a low GMAT score or a low GPA and will be left with unanswered questions about that weakness if you do not use the optional essay to address it. Rather than putting the committee in the position of having to guess at an explanation, take control of the situation and grab the opportunity to explain the details behind the weakness.
For example, let us say you have a weak GPA overall because you worked full time in your first two years of college, but your GPA from your last two years is much stronger. Not writing the optional essay means that you are hoping the admissions committee will take the time to search through your transcript, note the change in the GPA, and then examine your job history—then make the connection between your two years of full-time work and your subsequently lower grades during those years. On the other hand, if you use the optional essay to explain exactly what happened, you no longer have to simply hope that they will put in that extra effort and will know for sure that they are evaluating you using complete information. Likewise, they will not have to guess at the reason behind your low GPA, because you will have proactively filled in the story.
The bottom line is that the admissions committee is made up of professionals whose obligation is to examine all aspects of your profile. They are not punitive, but they are also not careless and will certainly note any weaknesses like those mentioned here. Keep in mind that these individuals are only human and are dealing with thousands of applications. Any way that you can save them time and effort by guiding them through the story of your application can only work to your advantage.