Originally Posted by soitgoes
2) practicality: in Europe, there are designated night trains which leave in the evening and arrive in the morning; couchette cars are only used on night trains. Amtrak has trains that run overnight, but they also run during the day. During the day, a couchette is not ideal for passengers.
well, usually you can rearrange the upper beds during daytime and have a normal seating compartment, same thing you can see on Russian style "Platzkartni" (open couchette) cars.