Sure, it can easily destroy the careful balance if its used, but it's very much someones own choice to use it. It's also good to have for anyone wanting to do some type of challenge run and needing special pokemon at the start of the game. Maybe a warning message about the balance when first creating an online account, but other than that I don't think it's necessary to restrict it at all. after all, this is a predominantly singleplayer game, so if somebody wants to play it in a certain way, why not?