Hard skill to learn for many, but many aces perfected it in conflicts like WWII, and often had the advantage because of that no doubt. Hans-Joachim Marseille had his deflection shooting down to a fine point, nearly perfect, with his shots landing starting at the engine, right through the cockpit, and past the tail.
If you couldn't do it, how much worse off would you be in a fight?
Now sims ain't real combat or anything like that, and I have played some, and I see that deflection shooting is not one of my strong points. Especially in a game like il Sturmovik with difficult settings on. I can still fight, but I think I could do better if I could shoot a plane down without being right on his tail or in front of him.