Surely there are conflicting reports about a lot of aspects of the admission process... some will say that the GRE is the most important factor because it's objective, comprehensive, and easy to interpret (just a number), but others will say it's your research experience and recs that prove your aptitude for real physics so they are more important. Who's right? Well both... some committees, depending who is on them in a given year, will weigh certain things more than others... The best thing to do is to shine in both!
Similarly for suck mails, surely it's possible that making a contact will win you the favor of that prof who may vouch for you later on (see Secander2!'s post)... though it's also possible he'll view your message as an attempt to kiss his ass at the expense of his precious time. The beauty of this forum is that all these varying opinions put all the cards on the table in a sense, and allow you to make a more informed decision about what to do in a given situation. Clearly the opinions on the forum thus far have swayed in favor of not sending these e-mails, but just take these as friendly opinions and always go with your instinct in the end.
My opinion is that it's best not to send them. Plenty of students will be messaging these profs trying to get a foot in the door, and frankly, even if you have a genuine interest in his work and a good reason to contact him, no matter how you word your message, he could interpret it as a suck mail unless you've had some prior communication with him, such as a brief chat at an APS meeting or an REU program.
But you can just as easily look at it like this: What's the worst that can happen? Surely the prof won't remove your app from consideration just because you contacted him... he'll simply disregard the e-mail. What's the best that could happen? He vouches for you and it makes the difference in the decision! So the "expected value" here is positive. Thus maybe you should do it.
Also, note that there are legitimate questions to ask a faculty member... for instance,
"Dear Prof XYZ, I'm applying this fall and I'm interested in XYZ subject. After perusing your school's website, I see there is work in this area being done in two departments. I'm unsure whether I should apply to physics or applied physics... what would you recommend?" I thought about sending e-mails because I was applying from a lackluster school to programs that were completely unrelated to the prior work I was involved with, but instead I just used my SOP as my chance to explain my reasons for choosing their program.
I'm just advising against these types of messages:
"Dear Prof XYZ, I'm absolutely fascinated with your work.... I've done similar research with Dr. XYZ at my school and have the following publications:
...........
I would love nothing more than to continue working on this subject in grad school. Do you think my GRE score ___ will hurt my chances of admission here?"
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