I believe that the advantage is so that you applications gets reviewed early on, maybe get an interview, and you get a definite answer (acceptance/waitlist/rejection) by a certain date, which is mid-late October. The other advantage is that you are increasing your chances of getting in (I don't know by how much though) because you are telling the school that they are your number 1 choice. If you are accepted, you are theoretically "locked" into going into that school and only that school. If it's anything other than an acceptance, you'll be "released" and then allowed to apply to other schools. With that said, you could take this route without being accepted, and still be able to make the November deadlines. Though I will say it is risky and is definitely something to weigh out.