I do as well, but point taken. We should provide less flippant examples.
I appprove.
is certainly better than Usergroups 
But @erlend_sh is on to something.
The confusing bit is that the groups don’t have a built-in conversation space. I was hoping that group messages would fill this gap, but they’re not quite there yet.
So, for the moment, I use a plugin to make groups & watch categories. It would be useful if that plugin I just linked to (originally by someone from the Discourse team and then hacked by yours truly) was expanded into a plugin with a UI, or even built into core.
But even that would not resolve the tension in having groups without a designated place for them to talk. Maybe there should be a way to link a group with a category. So, that for example, you could see the group’s category as a separate tab on the group’s page. That sounds like it would work for my case, but I don’t know if it would make sense for other systems.
In other news, I’ve settled on “private categories”, although my main collaborator objects to the “category” vocabulary. Maybe @HAWK was right all along