In his Zettelkasten Luhman used tags sparringly, in this video explains that Luhman used tags more as doors into the Zettelkasten, rather than as a way of grouping things together. Additionally, it makes automatic searching for keywords harder and forces you to look through your ideas manually. Which improves the linking of notes.

Sources⌗

https://www.youtube.com/watch?v=7TnUNN39NBU&list=WL&index=14