For example, I work in a relatively open space with two different teams mixed in. It's also the central hub for all the offices. So if anyone feels like chatting, in their office or not, or gets a bit boisterous, the developer's focus and productivity goes into the toilet.
It really is excruciating during those times.
I've had my own office before and didn't really care for it. The best work environment I've been in was a "double-sized" office (maybe 20x12?) with four or five desks against the walls. Pairing up meant just rolling your chair over. The door was most often shut to keep the noise out. Impromptu team meetings were quick and easy. Everyone in the office kept conversation volume low to respect the rest of the team. When there's only 4 or 5 people in an office you can make that stick. When you center a small company around a main area, where I'm also expected to work, that's a losing battle and you end up looking like the cranky old man who just can't stand it if other people are being cheerfully sociable.