In our department, almost all PhD students, plus a handful of EdD and masters students, have assigned desks. Some are in one of two grad students offices in our building, and a few are in a separate building that hosts an outpost of our department. We have a few students who rarely use their assigned spaces, but the majority of us are there several days a week. Most of us can do our work at home, at least 80% of the time. So why do we bother to come in? We come in because of the social networking that occurs.
Some of my friends and closer colleagues are people who sit in my pod. Some of them I wouldn't know as well - if at all - if it weren't for the proximity. Without it, I probably wouldn't be working on a project with Mr. Kindhearted this semester, and I wouldn't know some of the masters students at all. I'm even closer to students in the bullpen (our other office in my building) than I am to those in the other building simply because we see each other in the halls. Several professors come in to our office regularly, and they crack jokes, share news, or just check in. It's a rare week when Dr. Braxton doesn't have a new pun, or Dr. Crowson doesn't ask, "So what have you done for American education lately?" This shared physical space has done a great deal for building collegiality and camaraderie in a way that our program's attempt to create a cohort effect has not.
Without this interaction, my PhD experience would be much poorer, and I'd feel more out of touch with the happenings in our department. It was especially important early on in the program when many of us felt panicky with work and might have holed up in our own private bunkers otherwise. The casual interaction that occurs at our desks and in the hallways has built a shared experience much more than the formal interaction of the classroom. Much academic work is solitary, of course; at times all of us will have our headphones on, not to listen to music per se but to concentrate. But, as someone who is mostly an extrovert, I suspect I'd be much less productive in the vacuum of my own apartment.