It does not apply when aircraft are flying along specific narrow routes, such as an airport traffic pattern or jet airway.
[1] This implies that collisions of aircraft in free flight should be extremely rare in en-route airspace, whereas operational errors such as violations of formal separation standards should be relatively common.
The theory is also relevant in military aviation tactics, especially regarding targeting of aircraft and missiles by ground-based, non-guided weapons without visual spotting.
When coordinating corridors for friendly artillery trajectories through airspace, it is sometimes assumed (rarely, and for emergency expediency) that similar unlikelinesses apply.
If the target vehicle randomly maneuvered every few minutes, the chance of a hit would be extremely small, even if many projectiles were fired.