Yeah. I think you’re right.
I agree. Perhaps a pinned topic could make the join-a-group process a bit easier, or one that you direct people to the way you’d send the URL that you can’t have.
It comes up in different ways, I think, that may make searching difficult. I remember several such topics, but I can’t find them either.
Plenty of use cases, but the two most obvious ones for me are sharing a link on a Learning Management System or email list to get everyone in a class connected to a particular group in an invite-only forum, and using Discourse for a conference where lots of people might show up to a room and want to get logged in to a shared category in Discourse quickly. It’d be good if it either had a pre-set timeout (I bet invites have that already) or could be disabled easily.
Arguably you could get a mailing list’s user list and create bulk invites, but that’s cumbersome for a normal person and perhaps not everyone on the mailing list wants to play the Discourse game.