At main floor you can see all planes support facilities, 38 stands (mainly for big planes), taxiways, the 3 runways (top for arrivals and departures (GA included) and the both side runways only for departure of commercial flights), and the main terminal building.
First floor is managed to be the international flights hub of the airport when they will be released in next update of ACEO with passport checkpoints. Remote stands can get easily isolated for domestic flights at main floor.
-1 Floor is the baggage system heart and have some facilities to park service cars and serve as technicians headquarters with almost 40 service car stops to load and unload them.
At some point it was being selected to be implemented but when the devs started to look into the implications they decided to not implement it, think the above was never changed afterwards.