level 1 lesson 25- when sonia went over the conversation she said that ticket was used for a bus/metro and billet was used for a train/plane but she didn't explain why. Are these the only two exceptions when you’d use billet instead of ticket? .
From my experience, the reason why is based on the size. When you take a bus or the metro, it's a little stub, but when you take a train or a plane, it's much larger with more info. Another one I can think of would be a billet de théâtre.