There's the key-card system that gives access to approved individuals during off-peak hours. And the elevators of course. There are the thermostats that someone is in charge of in each tenant space. Also the lights, either always shining brightly or clicking off and on as spaces are occupied. Then there are all the parts and pieces hiding within the walls, in the basement and on the rooftops that make all those public-facing elements work reliably.
The funny thing is, for most people in a building, its essential role is to fade into the background, to just work. If you're aware of your building systems, it's likely because something is going wrong. You're too hot or too cold. One of three elevators is out of order or your key-card won't scan. Those are all symptoms of larger problems with the building's operations. If you're the building owner or property manager, the symptoms you feel are likely tied to increased operating costs resulting in decreased net operating income (NOI).