In Switzerland there are some differences between a first-class and second-class pass - on lake boats first class is needed to sit on the open-air upper decks IME (unless recently changed) and to sit in observations/panoramic cars on some of the country's scenic specialty trains.

But for the most part these are not enough of a matter to buy first class unless doing several of those.

Oh BTW - if you find second class too crowded or on a boat want to sit in IME the much more preferable first class sections and you have a second-class pass you can then go and sit in first class and then pay the conductor an upgrade fee - the difference between the first- and second-class fares.