He he, every once in a while this comes up. I couldn't find the original thread when Komodo asked about it, but here it is again . .
And no, you won't feel any difference in power if you leave the flap open all the time, not even at low rpm's. Won't damage anything either if you disconnect or "golf tee" it. This is to say that it makes absolutely no difference what you do with it, except for sound . . unless you're a ricer who believes a louder car is a faster one