Many applications invite submission of optional essays.
Typically, optional essays might ask you to articulate why you are applying to that school (“Why School X”), or they might invite you to discuss parts of your background that would contribute to the diversity of the incoming class (a “Diversity Statement”). Michigan holds the record, I think: they offer eight optional essay topics, although you are restricted to picking two.
Other schools have one-off optional essay prompt that you probably won’t find anywhere else. Georgetown and Notre Dame are good examples.
No matter what the optional essay topics are, submit optional essays only if the following three conditions are met:
(1) you have something interesting to say on the subject (content), and
(2) you can write about it well and do that topic justice in roughly one double-spaced page (execution), and
(3) that essay adds something new to your profile that isn’t already highlighted elsewhere (value-add).
“Why School X” Essay
If you are applying to School X only because it's a top school, or you are applying to School Y only because you have a better chance of getting in there than a more competitive school, then you don't have anything interesting to say about why you are applying. You might dredge up a few things to say about their "prestigious faculty," "excellent reputation," or "national placement," but that's not interesting either, because you could probably say that about any of their peer schools.
In fact, if the reasons you're giving for why you want to attend School X could be copied and pasted into the same kind of essay for its peer schools, then it's not specific (or interesting) enough to justify an optional essay.
If you're going to bother writing a "Why School X" essay, have something to say that really does distinguish that school (for you) from other wonderful peer schools. Of the different kinds of optional essay prompts out there, I treat only the “Why School X” essays as quasi-required, because I think it looks bad if they expressly invite you to talk about that and you have nothing at all to say. So put the work in.
Diversity Statement
Similarly, don’t bother writing a phony-baloney Diversity Statement if you don't have something meaningful to say about yourself.
You can and should think of diversity broadly, in terms of life experience that you have to contribute to an incoming class. Admissions officers are trying to put together an interesting mix of incoming 1Ls, all with different life experiences and backgrounds. Diversity in this context doesn’t just mean things like ethnicity, sexual orientation, etc. And yes, you are allowed to write about your race and ethnicity even after the Supreme Court decision. That’s in no way off limits for your essay.
Of course they are interested in underrepresented backgrounds, but if that doesn’t describe you, think about other aspects of your background that would add to the mix. Maybe you have lived and worked abroad, or are a national or world class athlete, or come from the art world, or you’ve overcome something really difficult that has affected and perhaps even changed how you go through the world. Those are all elements that would add perspectives in the incoming class. And that life experience will in fact make you a better law student and lawyer.
But that's not sufficient to justify submitting an optional diversity essay. You also have to be able to say something meaningful about that particular element of your background, and how it has shaped you in a substantial way. It's not enough to identify that you have that background; you have to explain why and how it matters. Always answer the implicit “so what?” part of any essay question.
This piece of writing also needs to be personal rather than abstract. If you can't discuss that part of your background in a meaningful, personal, well-written way, showing not just the "what" but also the "so what" (why it matters to you), don't submit the essay. Nobody wants to read generic mugga-wugga, especially when it wasn’t required. Then you’re just wasting their time, and that’s not the best way to get them to like you.
And even if you have those interesting things in your background, don’t submit a redundant optional essay. If you’ve already covered those aspects in our Personal Statement, for example, then your Personal Statement is also doing double duty as your Diversity Statement. Don’t waste their time with redundant essays. Any optional essay should add something to your profile that you haven’t already highlighted elsewhere.
Bottom line: You are much better off showing them one really great required essay on its own, rather than sending them a really great required essay plus a “meh” non-required essay. The latter actually detracts from your application and from the impression you're making. Don't dilute the impact or the quality of your great essay with something that is less than great. So make it great, or don’t submit it at all. Half-measures are the worst option.