PalenQ

A pass is not as flexible as claimed if you want an overnight train. You need to book in advance or it can be fully booked.>

misinformation - I have taken literally hundreds of overnight trains with a pass and only on rare rare occasions have I not been able to get on them right up until the time of the train so my experiences are very different than what kybourbon says she has experienced - makes me wonder how many overnight trains she has actually taken to say such a thing. Indeed many night trains I have taken even have Beds Free signs on their outside saying they have vacancies and I've seen plenty of folks just show up and get on.

PalenQ

Another aspect about hopping overnight trains using a pass - one great perks is the 7 pm rule - if you board an overnight train after 6:59 pm - and most leave after that - the next day is your unlimited travel day - thus you travel from 7 pm to the following midnight and use only one day on your pass (if a flexi pass of course) - for example take an overnight train from Germany to Copenhagen, arrive in the morning and then have all the next day to say go up to Oslo - you can thus go from
Germany to Oslo (or Stockholm, etc) and use only one day on your pass - now that lets you cover huge distances cheaply.