Applying early to med school helps your chances of admission. Weren't we arguing the opposite just last week? Well, as one cold winter doesn't disprove global warming, evidence that stronger applicants apply early isn't a reason to apply late. There are still several reasons that applying early helps your chances of admission.
1) More spots for you
The first reason is basic math - if you apply early, then medical schools have not yet accepted anyone, so there are more spots for you. At the start of the application process, medical schools are eager to start filling their interview dates with qualified candidates to make sure they can get the best class possible. And by applying early, there are more interview spots for you.
2) Med Schools want a diverse incoming class
Med schools don't blindly accept students with the highest grades and MCAT scores (that would make the application process far too easy). Instead, med schools want a diverse incoming class. They want a balanced class with respect to gender, race, geography, socioeconomic background, majors, past experiences, and undergraduate universities, just to name a few.
Why do med schools want a diverse class? Well, there are a few reasons.
a) Med schools believe that diversity helps the educational environment.
Read how Harvard describes the diversity of its incoming class: http://hms.harvard.edu/departments/admissions/applying/selection-factors/diversity-commitment
b) It's politically correct, and considering just how often medical schools are in the spotlight these days, it's important that they have a diverse class for the sake of appearance as well as for the legitimate educational advantages.
c) Med schools must justify their funding. For many state schools, it's important to prove to the state legislature (a huge source of their funding) that they're producing students who will serve diverse communities in that state. Read how the University of North Dakota aims to produce doctors for the rural parts of their state, including the underserved Native American population: http://www.med.und.edu/about-us/diversity-statement.cfm
Because medical schools value diversity, it's important to apply early. If you apply early, that med school may not have already accepted too many bio majors, or too many students from UCSD, or too many men. As a result, your spot has not been taken yet by someone else of your same demographic background.
3) Applying early helps you avoid costly delays.I can't even count how many students I've worked with who have faced delays from: a) lost transcripts b) a letter of recommendation that doesn't come in c) having to postpone their MCAT score
All of these factors introduce costly delays that compound the problems of applying late. By getting organized early, you can give yourself a buffer of several weeks (or even months) to deal with these problems as they arise and avoid trouble with completing your application.
4) Applying early helps keep you sane. It's no fun to feel behind in the admissions process, and pushing up against admissions deadlines can make even the most composed applicants feel frazzled. I would argue that this feeling hurts your chances of admission because:
you will feel overwhelmed,
you won't do your best writing when you feel frantic, and
you will get burnt out and end up not returning a bunch of secondary applications or something equally harmful to your application.
So for a variety of reasons, applying early still helps your application, and you should apply early if at all possible.