Superfoot Wallace has been known to say that the side kick is a very under used kick, and that it has tremendous power.
I just got back from the Virginia state games hosted by Master Robertson took first in olympic sparring two ranks above my own, green, having used primarily the a right leg sliding side kick, the right leg spinning hook kick, the left leg slap kick (a round house with your front leg), and the axe kick.
having done both though i would say that the biggest differances would be the stance, as a back stance is seen more often in ITF sparring, and the use of combinations in WTF are more common.