Back with newsgroups the general rule was to go from general to specific. You start with a general discussion group and when discussions about video games get annoying you create a games group. If then there are too many Baldur’s Gate discussions you create BG. If they are dominated by Baldur’s Gate 3 you create a Baldur’s Gate 3 group. If everyone is fawning over Withers you create a Withers group which of course will be flooded with discussion about the Withers’ tits mod, which shall get its own group.
Meaning you should create a group when demand is there and not the other way around.
This makes sense! I do think if someone is carrying enough love for Withers’ tits that they think they can keep a community active for a while on their own, they should go for it, though.
The traditional art community was just one person posting most of the time for ages. They aren’t doing that anymore, but that one person got it established enough that it still gets regular activity. Even if it hadn’t worked that way, there’s still a cool archive of artists I can go back through.