There's really no big advantage to having a FP to a show, except maybe Rivers of lights or Fantasmic.
Frozen sing along, Indiana Jones, Beauty and the Beast, Little Mermaid, Its Tough to be a bug, Lion King..really not much difference between standby and fast pass to where you'd want to try and grab a FP
With that said, if we don't feel like booking a FP for something else, we'll use it on Indy, Lion King, or Fantasmic