Building B sits empty for 16 hours a day while Building A sits empty for 10 with both being heated/cooled for 24 hours. The employee wastes 2 of their 16 available waking hours in the non-productive commute while incurring significant financial costs (lease/insurance/fuel/energy) in order to support this patently absurd activity. Similarly the employer wastes time and energy negotiating leases, re-arranging offices, purchasing AV equipment for meeting rooms in building B, etc.,etc., in addition to paying the likely enormously expensive lease itself.
The impacts on the environment, the number of hours of human life wasted in commute, the pointless buildings and associated costs to employers as well as the public infrastructure to support it (roads, trains, busses, etc.) are all incredibly wasteful. Surely, all of this could only be justified if physical presence had a dramatic impact on productivity. Yet, we cannot tell one way or the other if it actually improves outcomes.