[kkylin]

And ventilation, apparently. I was told [0] that it had been designed with open spaces in mind. And when research groups decided they didn't like people walking through spaces where people are working (esp working on hardware) and put up partitions and doors, that messed up the air circulation. Also, and somewhat ironically, I was told that despite the open design, people were runnning into each other less often than in the old Tech Sq building (with its much smaller lobby), missing out on serendipitous interactions.

[0] Private communication