Good points about application deadlines, but the Common App has made it easy to decide apply to whole lot of schools and/or to add a school to you application at the last minute. If you can bang out a quick essay for the school-specific prompt, and you don't mind the expense, your options are very open.
Very true about the Common App, but, the letters of recommendation - if not already in the works with teachers/counselors, can be tough to drum-up at the last minute, particularly since the Christmas break takes two weeks away where teachers/counselors will most likely not be working on these for anyone. Also, some of these essay prompts are a little more thought-provoking, if you've just banged-out a response, you're comparing your work in the RD pool to many applicants who may have really put effort into the writing.