Not saying they're required, just saying, well, here's the quote:
The school doesn’t ask for any optional essays or materials besides a resume. Chicago Dean of Admissions Ann Perry advised students not to send in information that is not requested, but a “Why Chicago?” essay or something of the like can be an asset. She said:
It’s fine if they want [to send in an extra essay] — they can add it to their personal statement. I am a fan of addendums. If they feel there’s something they really want the admissions committee to know that already isn’t in their application in another way, addendums work in that way. Sometimes I think about going to a Why Chicago question; I haven’t yet, though.
I didn't do it myself. [edit: it's very ambiguously worded, imho]