I wrote a longer response but it got deleted (oh noes!).
Basically, it'd be useful-but-not-necessary for admitted students, just to be 1) reassured about basic things (yes, it's totally possible to live in New York, yes, students from our school total get jobs) and 2) to figure out who might be good to work with, so that they can figure out i) who to meet on visit day ii) whose graduate students to get "the dirt" from on visit day.
Sadly, for students just applying it might be less of a useful system. All Columbia students have profiles listing our email addresses, so I get emails blast emails sent to every single one of the graduates and more rarely students tailored to me and my research interests. The ones tailored to me are good, the blast emails are more asking questions like "Yo, these are my interests, does anyone at your school do that stuff?" and "Bro, what's the secret to getting in to Columbia??" I've replied, mainly telling them to come to Grad Cafe, but unsurprisingly none of those students get in. I feel like those dumb questions from lazy people would outweigh the good, thoughtful, considerate questions like "I like Joshua Whitford's work. I'm super interested in organizations and manufacturing. Do you know if he's tenured?" or "I am interested in working with several faculty at Columbia, but there are one or two that still at NYU/Princeton/The New School/CUNY whose classes I want to take. Is that possible?" or "Is it hard to pass quals at Columbia?" (to be clear, I have actually been asked the first set of questions via email, but the second set of questions are the better type of questions I hope I could answer through private messages).
Just to answer those "good questions". 1) Josh is great and just got tenure! I haven't worked closely with him, but people who have love him. Because he just got tenure he hasn't chaired any dissertations yet, but I think he's ready to. 2) Yes! Starting in your second year you can take classes all over the consortium (starting from your first year if you have a graduate degree in literally anything) 3) We got rid of quals! And masters theses! We now have "purely professional requirements": i) submit a grant application ii) submit an article to a journal (neither need to be accepted) iii) present your work somewhere, anywhere iv) write a field statement in the style of an Annual Review article and v) dissertation prospectus (probably like 10-20 pages outlining your research agenda--there's a class for writing this your third year).