In my opinion the only good thing it does is to create copies of already existing communities, so basically people tend to follow one community or the other and it divides the people who could be active.
If you want to create a community that’s similar to one and for some reason you don’t want to be a part of it, find another name, if you can’t find another name, create your own instance. So if Lemmy is federating now we could have /c/worldnews, /c/world_news, and the same applies to every other instance that decides to do the same. In my opinion this only segregates people.
The same applies to uppercase letters, which Reddit uses but luckily Lemmy does not, imagine how many copies of a community could be created if you use both.
Absurd example, but there is a city named “Chicken” (It actually exist !) A community about cooking chicken : eatin_chicken A community about places to eat in the city of Chicken : eat_in_chicken
I mean… I think there are a couple of valid examples, I think it would make more sense to create a community named /c/chickencity and there you’d ask for places to eat, though. But let’s say it’s a valid example, in my opinion the pros are more than the cons. How many copies of communities can be created by adding the _ and how many communities will need to phrase their address in a different way because of it?