It allows rapid transportation all over the world, and it can destroy an enemy at minimum risk, especially with modern unmanned attack planes like Predator.
Why Is Aviation Important?
Before aviation, a trip across the US took 3 days if you were lucky enough to be on an express train. It also took three or four days to cross the Atlantic between Europe and North America on the fastest ships and many weeks for other routes. Sending a parcel on the slow boat to China might have taken a month.