There might be cases when you want to 'retire' a tag rather than 'edit' or 'delete' it. Which is, stop using the tag but keep it at places where it is already used. In such cases, one can disable the tag & it will not appear anymore on 'Give Feedback' pop-up.
Thus essentially if a tag is already associated with any feedback, Employee Success lets you disable the tag as deleting it is not possible.