While I do think it's okay to talk about electives just know that A LOT of people do this and I think there's a good and a bad way to do it. Don't write about "Why School ________" and then have a random paragraph in there saying "...and I want to take this elective with so and so professor along with this other elective with so and so professor." I cringe when I read something like that in people's essays. I think people go this route to try to show that they've done their homework on the school's curriculum, but if done incorrectly then it makes it look like that you just went on the school's website and pulled the information from there. Think about the larger picture.
1.) You will only be in said elective for 1 semester, yet your whole b-school experience will be 2 years long (assuming you're applying to a 2 year program). So now you're using valuable essay real estate to speak about that.
2.) Also, if you've already identified your long-term goals, say "Banking" then saying that you're excited to take Finance course ________ may simply be obvious, especially if it's a popular class at the school.
3.) Lastly, if you're applying to a top program then I'd say a good amount of the electives are similar so if you choose to write about one that REALLY excites you, then make sure you've done enough research to come up with incredibly good ideas why you want to call it out in an essay.
Failing to pay attention to these points will make your essay sound like a myriad of other ones that come across the AdCom member's desks. Just keep those points in mind! When I was writing my essays last year, I wrote a whole essay about a class that I had sat in on at Johnson. It wasn't even an elective - it was a core class, but I wrote the essay in such a way that I talked about the interaction between students within the class and how I felt while observing and what that said to me as a whole about the environment at the school.
