"When we say optional, we really do mean optional. The Committee will in NO way hold it against you if you choose not to answer any of these questions. (Maximum 250 words.)"
I wasn't planning on it. If I do, I'll probably do a funny video.
I plan to write them all. Like @"Cant Get Right" said above, they are "optional" but I think any serious candidate should write them. That's the general advice from admissions professionals, too.
... "Why This School" essays, "public interest" essays, or essays like UCLA's "programmatic ... .). A productive goal of your essays should be to prove that ...