Some people have been asking which communities they should join first, so I posted some remote communities you can subscribe to on the sidebar on the homepage :)
There's also this universal community search tool you can try using. If you find a community, just copy its URL and paste it in /search to subscribe to it here. This just goes to show that while there might not be many local communities here on lemmy.one yet, the beauty of the fediverse means that doesn't matter!
They are only de-federated from lemmy.world and sh.itjust.works
Lemmy.one is still federated with those two and beehaw.org
That means it has no impact on us at all, afaik. I'm no pro but I just made a new account, after having a beehaw one, on this instance specifically to see if I could still see everything on all three, and I can.
It has an impact - you can't see posts or replies on beehaw communities by people from lemmy.world, even if we're federated with all of them. Only people from lemmy.world can see those (but they can't see anyone else's).