Inside the aerosol can, there is a mixture of pressurized solids, propellants and solvents. By pressing the spray nozzle, this pressure and thus the contents are suddenly released.
In the same moment, the propellant atomizes within a split second.
Every single drop bursts into many midget droplets.
With no other technique you'll achieve a comparable fineness of droplets.
The result: The active substance (paint) will be applied - more economic, more even, smoother and more dry.