In my case, I have an acceptance to a school that I really love and gave me a massive scholarship before they even determined my need for aid. I find it highly unlikely that the state school (OOS) that I was accepted to could make an offer that would be able to trump what I already have from a school that I like far more. Truth be told if I had received an acceptance to the first school earlier, I wouldn't have attended the interview at the other school, but thus is the process.
But point taken...I guess it doesn't necessarily help out other applicants to relinquish your spot, but it will at least help the school know whether or not you are seriously considering them. I guess my case is different in that I received a scholarship along with my first acceptance.