Not 100% on this either, but on the magazine settings it has options to include all posts from a tag, so in theory tags can be used to post to multiple magazines if the magazines are set to receive those tags. I haven’t seen this working yet but also haven’t tried to make it work.
I’ve set up a couple magazines to use this feature so I’m hoping they’ll start auto-populating with content from Fediverse maybe. Will see.
On Kbin if you go to add something, a link or an article or whatever else, there is an entry field for tags and an entry field for badges. Still no idea what badges are for.