Reservatins Berlin- Prague and Prague-Munich are not mandatory but I strongly recommend a reservation. I am sitting on the train from Berlin to Prague  right now and it is totally overcrowded, partly due to an earlier cancelled train. My daughter and I had to stand half of the way even though we have reservation as the seats were double booked. 

When there are too many people on board they ask everyone with out a reservation to leave the train and they get the police to help them to get people off the train. This has happened quite often recently on the trains to/from Prague. Our train was delayed by 30 minutes due to this.

The best way to make reservations from Berlin to Prague is bahn.com. Use the option "Seat only"

ok thanks for the information, but i just want to know why now the brussels-midi> amsterdam central route is compulsory.  the site says something different every day and I wanted to know from an expert what are the stages of my journey, where I have to make the obligatory reservations, thank you.  my route is London st pancras - Brussels midi on 07/08 where I made the compulsory reservation, then after the stopover in Brussels the train leaves for Amsterdam, is it compulsory here too?

Yes Eurostar and Thalys trains have always compulsory reservations. 

Between Brussel and Amsterdam there are every hour Intercity trains that needs some more time, but no reservation needed and not possible. 

You canNOT use €* FROM BRU to AMS

TLS suffers from loads of cancellations right now-and is also very overpriced for what you get on this fairly short ride. So that means the hourly yellow/blue RES-free combi NL/BE INtercity.