We use them extensively in our agent framework at work for all sort of things. You can make up whatever you want, if the tags are semantic enough it just gets it, or you can add a bit of explanation about it in the system prompt or whatever.

  - Circuit breakers when it seem like it's stuck in a loop
  - Warnings about running low on context
  - Reminders about task lists (or anything)
  - All sorts of warnings about whatever