What others do shouldn't influence whether you write this optional essay. Many people unknowingly write about irrelevant and inconsequential thingsthat end up hurting them. Many others choose to leave this blank as they felt that the rest of their application was sufficient for evaluation. Without knowing how others' applications were perceived by adcoms, it's hard to glean much useful data in my opinion.
The general consensus is that you should leave this optional essay blank unless you have something actually important to write. Most applicants should be leaving this blank (unless the optional essay explicitly asks for diversity, adversity, etc, that's a different story). As I've said before, the decision to include something in an optional essay needs to meet a higher bar than that for required essays.
Keep in mind that when everything is said and done, most applications will consist of ~20+ essays and letters (more or less depending on whether a committee letter was used, and how long the secondary was)... Any information that didn't make it into one of these essays is likely either not that important, or was only the 16th most important thing about you, which is unlikely to change anyone's decision on whether to interview or accept.
Writing an optional essay may also call into question an applicant's judgement and decision-making if they choose to write about something inconsequential or irrelevant. There's also something to be said for respecting the reviewers' time, as many of us volunteer to do this (though this last point may vary by institution). Hope this helps.
