My friend and I are travelling from Paris to Munich. We are buying a Eurail Pass. We are visiting Belgium, The Netherlands, Germany, the Czech Republic & Austria. If we make reservations for a particular train, is there an additional cost? Do we really need a reservation? We plan an overnight train from Amsterdam to Berlin. We are travelling in September 2014.
Generally, if you want to travel on any fast trains, yes. On regional trains, no. In France it is mandatory on TGV's as they limit the number of passholders they allow on any given train. Definitely on night trains. and if you want any type of couchette or sleeping compartment, you will pay full cost of the accommodations.
See here: https://ricksteves-cms.herokuapp.com/travel-tips/transportation/trains/reservations
If the trip is roughly Paris-Amsterdam-Berlin-Prague-Vienna-Salzburg-Munich, then the legs that require reservation are the Thalys running Paris-Amsterdam (about $55 per person in 2nd class or $95 in 1st class) and the night train Amsterdam-Berlin (price dependent on type of sleeper). How to Look Up Train Schedules Online gives you the DB train schedule link and tips for using it. This is the best resource to confirm which departures are "Subject to compulsory reservation."
I am by no means an expert on trains, but I too was thinking about buying a Eurail Pass. After getting some great advise here, I look up the difference and purchased my tickets in advance. Yes, you do have to stick to that schedule once you've bought your tickets but if you're looking to save money, then it's a good idea to buy in advance. I ended up saving about 1500 dollars buy making early reservations. Something to think about. Have fun on your trip.