Man, Terry, you are kicking some butt with these thought provoking threads. Good job *bows*
Anyways, for me, it depends on the situation. I always strike with my heel, but as for set-up, it depends on if I'm sparring, breaking, kicking the air ... But even that doesn't matter. I have done breaking with a front leg side kick, regular side kick, step behind side kick, flying side kick, ect. The same with sparring.
In sparring, it depends on when and if theres an opening, and if the timing is right. And what my partner is throwing at me. I use my front leg side kick as a "jab" or to stop my partner in their tracks, or I use the rear leg side kick to "power" them away from me, or to I perry and kick them in the ribs ... it all depends on them, the timing, ect.