Trail characters are the ultimate way for both new and old players to test out classes in PvP/PvE to determine whether or not they should invest their time, money, and effort into re-rolling to another class. Not having them is extremely painful to try and find a main character you truly enjoy. 

If the concern is that too many people will spend their time in the Battle Arena, then I think it is unfounded. It will not stop the core playerbase from going out and wanting to progress and explore the world of Black Desert