I used to be an individual office partisan, but after working for a coupla years in cubes with walls that come to a sitting person's neck, I find that there are a lot of benefits: I can just turn (and scoot across my cube, if necessary) to ask or answer questions of a co-worker; I can hear when people begin chattering, which is a sign that something is going on that I need to pay attention to, like the site being down or a discussion about some coding question; I have long lines of sight in at least some directions, which is nice for my psychological well-being, especially in contrast to some office without an outside window.

The main thing, though, is serendipity: overhearing party A ask party B a question to which party B doesn't know the answer, but I do, or hearing people planning to have a meeting I'd want to be in, but which they don't know I'd want to attend, etc. A closed office would be slightly more useful when head-down coding for hours or days at a time, but so much of my time as a developer is spent chatting about coding, helping people solve language or environment problems, talking with users who wander in looking for help, and other miscellaneous interpersonal activity that a closed office would hamper my job quite a lot.