The flaps are pretty much always open anyway. It's only under very low load (low rpm, trundling around town etc) that they are anything but fully open.
People remove them as the flap and the flow divider in the head present an airflow restriction. As for gains, in terms of numbers it probably won't net you much unless maxxing out a Stage 2+ K04. Does make some lovely noises, pops/bangs since fitting though, especially with Meth :)
