The advantages of air are
1) speed
2) some units can not effectively shot at air
Speed is only useful if you know where to go.
This requires situational awareness.Good airplayer moves around the whole map, that brings responsibility.
Must decide where to fight and where it would be waste.
Compare to groundplayers who can do okay by 'staying in their lane.'
Air can boost effictiveness of team and turn a failing attack into success. Say your team attacked something big but the target survived with little health. (Commander, Fusion, Strider, turrets)
Then airman must
see the opportunity of easy kill and finish the job.
If someone has to point out those opportunity-targets then it will be too slow: Target moves out of sight or is healed.
Air is also best for scouting/LOS. I like when airman keeps stuff wiggling around in front of my army, it helps to go around defenses.
When enemy radar dots start to amass on a hill then airman must go look what is happening there.
Good airsupport is like playing with global-LOS cheat.
On defense air can move over whole front and help out where it is most needed. But airplayer must be able to predict situations, disarm/EMP bomber is useless if it arrives too late.
Sometimes enemy units break through defense and all ground units are too far away.
It might be only a few raiders but even those can quickly kill lots of eco if they get into base.
Airman must recognize such situations and decide to perhaps 'waste' a few bombs on tiny raiders if helps to protect eco.
Airman also has to switch between anti-air / anti-ground and often there is only one air player on team. So if that player made a wrong choice then there is nobody as backup.
All these things require awaress of the whole game.
It does not require constantly high APM but at times demands quick decisions.
Often it is subtile things, difficult to explain ingame.
Of course an airman can also just do 2, 3 mass-bomber-suicide-attacks per match. But good airplayer can do so much more.
