In some places I've worked in, the space saved by open offices was used for couches, ping pong tables and other perks. The companies didn't end up saving space, or not at the rate that they could have. Whether that's a net win for productivity is unclear.

However, when you're dealing with a behemoth that views 2-ply toilet paper and store brand coffee as luxuries the employees should be thankful for, it's easy to see how these savings would motivate the move to open offices.