The benefit could be argued it’s not as bad as “ethnostate”. Really the default is between ethnostate and racial segregation. So it’s “beneficial” compared to being German and punching Frenchmen. Or being north German and punching south Germans. (Being more honest. If there is a benefit in game, it gives you a little more authority in the government to pass decrees as well. The more racist your (accepted) people the more they accept what you tell them. That’s not worth it though. There are better ways to increase government authority too. Also America kind of sucks for this more than small nations anyway.)

You want to get to multiculturalism, which eliminates most discrimination effects. It’s only the mid game ,where it’s very hard to get to multiculturalism, where you benefit from having 2 accepted cultures. If the accepted cultures are both European it makes no difference and there isn’t a benefit to having 2 cultures. It would be pretty white washy if they removed racism from a game in the 1800s. One of your goals should be to reduce it as much as possible.