Anyone who has known me for a long time, has heard me poke fun at flying kicks. I had to learn how to do various flying kicks to get my first degree black belt but I have seldom had use one in a fight. I had lots of opportunity to fight for the couple of years I was a bouncer at a bar.
Ok… I can think of one time when a flying kick worked, I was chasing a couple of guys down the street that had thrown something into the bar… startled I ran out and saw two guys running away. I was young and gave chase. They were just trying to get away in a car they had just opened and I jumped the last few feet to smash the car door (with a flying front stomp kick) into the driver. That caught his attention and he had to explain himself.
Mostly though, I have ridiculed flying kicks because one cannot change direction in the air (a real disadvantage in a fight). Here is the highest flying side kick I could find on the web executed by a William Fincher. 
Picture from: http://www.kimsookarate.com/gallery-present/paraKick.htm
