Yeah, I see that userid is included in the tags, but if you want to see all who are currently in the chat you use that API. Also you can call https://github.com/justintv/Twitch-API/blob/master/v3_resources/streams.md#get-streamschannel to get the viewer count but not the chatters.
Also I am pretty sure every chatbot that has any kind of point system that gives you point at random time intervals uses the TMI api as well.