Topics only help to keep things organized and better than other chat systems if they are reusable and long-term identifiable. If people create a new topic like e.g. "Wednesday meeting" or "The printer does not work" every time they want to say something you end up with same mess as in other chat systems. Also it's quite human that discussions get offtopic. Zulip has nice support to continue in or move the discussion to the right place. But to my experience only a couple of geeks uses them.