They do, admittedly provide a small amount of extra flow. But at the expense of filtration efficiency. You might see a small gain, 1-2 hp(even still that's within the margin of error for dyno tests), but for the most part really only make the intake a bit louder. As it stands, OE filters are generally sized pretty well for their application. Think about it, if they weren't, you'd have issues both with the efficiency of the engine and the pressure drop causing damage to the filter. They're not exactly designed for a large pressure differential. With that said, if you're doing something that needs more airflow, you wouldn't be using a drop in filter anyway. You'd have a proper custom intake setup