I think the lines and angles are supposed to help you judge in what direction and how much lead you have to pull, taking into account angle, speeds and distance of the planes. But by the time I have calculated all that and 'read' the lines of the gunsight, the con has usually reversed on me and shot me down.
I kinda shoot with empiric intuition. Or so.
The gunsight only makes a difference insofar as there are some that are so 'dense' that they obscure the view a bit. But thats also a matter of being used to.
BTW, im using the Waffle-Sights. For no particular reason, apart from eyecandy maybe.