worriedDad

I have conducted these alumni interviews for 25 years for my alma mater, Brown. They are not inquisitions, just conversations. You should view this as an opportunity to present things about you that just didn't fit into the application. Another dimension about you. And also for you to learn a bit more about the school, who has gone there, what THEIR experiences were, and what they (the interviewer) were able to do with their education. How did Brown (or other school) influence their life? Ask questions and be an advocate for yourself, but diplomatically. Like any other meeting for the first time, it is also important to be interested in the person who is talking to you, too. Just make sure you know why you might want to go to that school: do your homework on that.
As to the importance of these interviews, I feel they serve primarily as public relations for the school with the prospective students, not for admissions decisions. Oh, when you are on the edge of admission or not, they might take a glance at them to see if there's anything in there to help them learn a bit more about the candidate. As I said, another dimension not on the application. Overall, I've never seen any direct relation between these interviews and admission. Admissions reality is NOTHING like portrayed in the movie RISKY BUSINESS! Other stuff is more far more important. So relax, and try to enjoy the process of having a school make a fuss over you!