Lots of kids participate in those events because it's another chance at a medal, and if they are nervous program skaters it might give them a chance to shine at elements they actually are good at, but freak out with when the music turns on.
For 30-45 seconds of skating, I think these are money maker events, as compared to programs, but they are fun to just have another chance to do your best. When I've done them in the past, we didn't really practice for them, except one day practice right before the competition to determine the order of the elements, so they don't take much lesson time to prepare for.