It's a trade-off. Closed offices make deep thinking easier; open floor plans make communication easier. Ideally, you want both, but how do you get it?
At times internal coherence of e.g. a planning / architecture team is invaluable. And if such team is embedded in a larger space with related people around it - fantastic.
Most spaces however serve more than one goal. An externally focused organization will want loose coupling to the inside. The last you want to happen is all sales guy jumping on the most promising prospect.