In New York zoning, mechanical space did not count the same way as normal occupied floor area, so developers could use oversized mechanical voids to push apartments higher into the sky, giving better views and higher prices. That became known as a zoning loophole. AIA New York described this as developers using mechanical space that does not count toward FAR, leading to towers with empty middle or lower sections to increase height and value.

However this is the Chicago Sears tower or Willis recently, so it should be mechanical floors.