In general, and commercial aviation flaps are to increase the rate of decent, without an increase of airspeed. In combat avaition they are used to tighten turns, increase rates of climb, induce overshoots. The Corsair is a great examle of it, without flaps it is a good turner, with them it will turn with just about anything in the air. You can use the flaps at 250 in a hog, and you can blow the gear at over 300, and slow it down by 30 mph to get it into your flap range, and then crank it around, get the Zeek that is on your butt, and put rounds on it. Coming into the carrier, get full flaps out and hold 110 and get it down, turn final and fly it to the deck at 90mph, flair catch a 1 wire and get back into the fray,without having to back up to the end of the deck so you can get that Heavy hog in the air.