For example, if state buildings require 10.000 Megawatts but Power plant output is only 5.000 Megawatts all the buildings in this state will be performing at 50% of their level, excluding Military academy and Power plant.
This building determines the time needed to travel to/from the Moon.
Decreases (unlike Missile system) attacking side damage in Ground and Troopers wars in case of positive difference of Airport levels. Just like with Missile systems, only difference up to 300 points is taken into account. You should see damage formula for more info.