Even just starting out, I've wished to be able to create a Simple Grouping. I'd have a Cultures grouping to describe those setting features.
Cultures
- Culture A, B, C...
-- Language
Languages(s) and dialects of the culture
-- Thought
Religion, philosophy, ethos, codes, laws
-- Food
Typical diet; interesting or unique food items
-- Art
Common art forms and famous works
-- Leisure
Sports, games, etc
-- Artifacts
Ethnic cool weapons, characteristic items of manufacture, "tech level"
It seems pretty common in setting materials to have any number of nations, races, polities, subcultures, and so on. This would give a place to put all these kinds of topics.
You could make all cultures "Groups", but then broad cultures of the world get mixed in with story-specific organizations and small bands -- this Mafia, that wizard guild, those adventurers. It seems like it will get hard to sort out. You'll need a lot of scoping tags.
(There's usually a bit of conflict between a hierarchical scheme like the topics, and a tag facility. Anything you can do with the hierarchy you can also do with carefully assigned and scoped tags. But it's usually easier to get it right and to browse if you have a hierarchy. The chief problem with a hierarchy is that complex data rarely falls neatly into one exclusive tree. You usually wind up wanting something to appear in multiple categories and sometimes multiple levels of the tree. Browsing by tags is hard if you don't know the tag ahead of time; the tag list is flat, so they're all equally useful and applicable as far as the UI is concerned -- but not so for someone searching for some information.)