I'm not sure how useful it is to email professors when you apply. Sometimes they don't get back to you, sometimes they do with nothing interesting. But then again, once in a while you get a helpful piece of advice, or a professor who's even willing to write to the Admission committee about you. It doesn't always have the impact you'd like but it can't hurt. So basically you have nothing to loose by writing them, it might not help but it certainly won't penalise you. I'd advise people to do it.