Notice there is a black border in all maps. By entering it, you're unit becomes invisible to the enemy, thus granting you invulnerability. This is a perfect cheat for an Air Drone base camp to destroy any enemy aircraft that comes out from a Hangar that could possibly be built near this black border. You can also use other units to base camp, a Harkonnen Air Defense would be a perfect example, as it can destroy enemy structures, forcing them to not build near the black border.
If you do not understand what the black border is, then check around the map, noticing a blacklish area that cannot be revealed. You can enter this black border only a little.