on cold startup the flap opens and makes the car suck hot air off the exhaust manifold. then when the car gets to a certain temp it closes the flap allowing the car onlt to suck cold air from the front of the airbox
its not really nessecary unless you live in somewhere that has drastic temps like -15 degree etc
Thats nearly right.
If i remember right there is an intake air temp sensor which controls the flap via vacuum from the inlet manifold.
If the intake temp is below a certain level then the flap starts to open, and so opens the intake to hot air from the exhaust manifold shroud.
Agreed its not really necessary in this climate.