Thank you to everyone for your replies! Now, forgive me for continuing to play devils advocate
The issue of sending it before they give interview is then what do you do if you get stuck in the cycle? Sending when you're stuck forces many schools to relook at your application, and the more times they look at your application the more likely it is that someone will see something they like about you.
But, didn't you send more than one LOI? If you're going to send more than one, why not start early?
The other larger issue of sending before interview is that A LOT of students learn most of what they know about the school at the interview. There is huge changing in what people want and where they want to go after interviews. So if you're telling a school "I love you and will go there no matter what" before you've ever been to interview it sounds like a lot of smoke blowing and the school knows from experience that lots of people change their minds after seeing the school and really learning about it.
Well, I hear repeatedly "medical school is medical school" for the most part, so although I'm not going to say that to any admissions committee, that's not a deciding factor to me. My primary concerns are having my wife close to friends and family while I'm busy with school, staying in state, etc.
And what you're talking about is basically early decision. Unfortunately sending an LOI is by far no guarantee and doesn't get rid of the boloney of interviews and secondaries. If you really want to get rid of that you would have to do EDP.
Well, with EDP you only get to apply to one school, and if you get denied then you have to wait until October to get into the regular applicant pool... that sucks unless you have insane stats.
If I had an acceptance in the early winter then I could avoid the costs of interviews, etc, etc, etc. You're right about the secondaries though. I'm pretty much stuck filling those out.
In addition to what other people have said, what about the money aspect? If a school knows you're going to go there, no matter what, then I'm guessing you'll be less likely to get lots of financial aid.
Staying in state = huge financial incentive. Probably better than most finaid packages
My wife's income suffers when we leave the state and the cost of school will double.