Since I like you guys so much, I"ve decided to help you folks out here.
I"m a program director and read these threads occasionally. They're pretty funny actually. I'll break my code of "reading only" this one time and give you a PD view.
Why do we ask this question? Of course the answer is dependent upon the program director, everyone has their own reasons.
I ask this question occasionally because:
1. It's an easy ice breaker: I don't really care where you're interviewing so much as the programs but I'm interested in you and this match process is alot of travelling and expenditure so I ask out of respect for your investment. I don't ask it of everyone, and I don't have a strategy other than asking it whenever it seems a good question during our discussion, which is the same with just about every question I might ask. It's a conversation folks, don't read too much into it.
2. Sure, when you answer, I get a sense of your competitiveness; but I know that already since I've got your ERAS information. Don't read too much into this rationale. However, it does also give me an idea of what your interests are and your priorities. If you are a mountain biker and you're interviewing at Miami and New York City programs, for example - this gives me some insight into your interests and the weight they play on your residency selection. PDs don't hold these concepts for/or against you, at least I don't, it's basically just another element you can tell me about yourself that I can't find on the ERAS information. Also, it tells me something about your fit for my program.
3. I love the discussion about program directors talking to each other. Everytime this discussion comes up in these threads, it's just great because the misinformation is really astounding. Yes program directors talk to one another. Mostly this is when I call the PD at your school to ask them about you. I only do this if you already have a letter of reference from this person. Some program directors do this, others don't. Most PDs likely do it for a few just to get some final information. Occasionally it affects your standing on the match list, particularly if your PD says, "Oh XXXXXXX? He's really great! And we're going to keep him here, he's definitely going to stay with us here in (you fill in the blank) and we just settled that the other day." Really, most PDs simply don't have the time to call a bunch of others. We call a few, mostly people we know well, particularly if there is a "pipeline" between a medical school and the program that is a mutually beneficial relationship. A pipeline is basically a medical school matching someone in EM into a certain program each year, "Who's it going to be this year?" Remember, I'm working on placing my medical students as well, this motivates me to call on their behalf more commonly than inquiring about applicants.
4. Asking you to compare programs? This is another great one, lots of fun reading the replies there. See #1 above, don't read too much into it. I ask this question of some people, usually because it tells me your priorities and interests. "Tell me something about this place you rotated?" When you then say it was too busy, and I know my program is busier - then I"ve just gotten some useful information about your fit. Maybe you reply that you liked the program because everyone was taller than 6 feet. Again, useful to me because I know the people in my program are shorter than 5 feet. No, PDs are not looking for you to bash your program, and even if you did (this rarely happens) then we'd be unlikely to communicate it back to the program, at least I've never done that since our discussion is confidential to a degree and if I"m asking you your honest opinion, of course I"m not then going to come after you for giving it to me.
A final comment. PDs in any specialties are like the birds up in the sky (I'm sure I'll get roasted for that one, but I like birds, particularly flamingoes so the comparison comes to mind). We've all got feathers and wings which in this case are fortunately our love for Emergency Medicine and for residents. However, some PDs are big, some are small. Some are aggressive, some rather not; etc, etc. So don't characterize us as a group. And, just because one PD asked you something peculiar, or is strange, or whatever doesn't mean we all are. We're a diverse bunch with a diverse rationale for doing the things we do.
Find a PD that suits your style and interests, and hopefully a program that does the same and rank it #1.
Good luck.