[spolsky]

Wha? That's ridiculous.

Mostly, Facebook just copies Google's playbook, usually because so many of their managers came from Google. And a part of Google's playbook is that not every good developer wants to live and work in Silicon Valley, so you simply can't hire enough good developers if you only have one location. By the time a company has hired as many people as Facebook, they've failed to hire hundred of others who, for one reason or another, don't want to leave New York. Maybe their wife is in medical school or their husband is a quant on Wall Street. Maybe they like the arts, or nightlife, or walkability. Whatever it is, Silicon Valley is not for everyone and at the rate that Facebook (and ebay, and Google, and Twitter, and Microsoft) need to hire programmers, they have to consider a few out-of-town campuses.