I agree that it's theoretically better for applicants and worse for programs if people are going on so many interviews. Programs can only interview so many applicants, and if their top 100 people have each interviewed at 20 programs then their level of certainty about getting any one of them decreases substantially. Programs that are used to being in the top 3 of most applicant's ROL could potentially end up much further down if these applicants are interviewing at a wider range of programs geographically. Meanwhile the applicant only looses money from travel for visiting all those places, but also shuts out other applicants who might be ending up with fewer interviews. Your chances for matching at any given place go up if you assume that people will have different priorities in how they are ranking those 20 programs. Otherwise the top 5-10 programs would look pretty much the same as they always have and the next 10 might have to go farther down their lists than in years past. Thankfully many of us visit the same programs and don't rank them exactly the same!
That said, for those of us who over applied and found ourselves both having too many interview offers to juggle, and also being on multiple waitlists, it's a pleasant surprise to be wanted, but somewhat logistically complex as far as the decision making process for when to cancel interviews. I like to think that all things being equal, once you have the interview spot (waitlist or first round), it's your chance to make the case for yourself and for them to realize why you are a good fit for their program, particularly for places where you were a good fit to begin with but maybe were missing a CK score or something else that prevented a first round invite.
As I've gone through the interview process I've thought a lot about what my priorities are for life in the next 4 years. I found myself going through the remaining interviews I had signed up for and canceling all of them that required significant travel and that I was likely to rank below most of the programs I have already interviewed at. It feels weird to cancel interviews at places that might theoretically have more to offer than some of the places I've already visited, but I like to think that someone will be really excited for that invite. Hopefully some of the people holding onto interviews at some of the places I'm still waiting on closer to home will feel the same way. In short, if you already have visited at least 9 programs you are planning to rank, don't be afraid to cancel January interviews now. Consider it your Christmas (or whatever holiday you celebrate) present to your fellow applicants, and also to the people working at the programs who then don't have to place people in spots at the last minute!
