Some people also aim the dot sight down ever so slightly, so that it's spot-on at around 100ft, just a little high in the 25-50ft range, and compensates a bit for drop in trajectory at the 150-200ft range, where AEGs start to lose hopup. This can be tricky to get "just right" but if your gun has good accuracy it can help you once in a while when your're trying to hit targets smaller than a torso, like someone's arm/leg sticking out from behind cover.
But like Strelok said, lots of people just ignore it and never really notice. We're not shooting bullets here
