There is a messages tag with 67 questions and no excerpt/wiki, used for any sort of message. It seems rather ambiguous to me: there are plenty of specific kinds of messages that have more useful tags:
And so on. When it's not being used in place of a more specific kind-of-message tag, it's being used like the text tag was, to indicate that the question is about specifically the text/message displayed within some context (example: Don't say "Comment if you're trying to respond to an answer." when there's no answer, after clicking on "answer your question").
(9 questions with the tag use it to refer to the messaging function within Careers, which is not on topic here)
This doesn't seem to be useful at all to me, but I'd be open to being convinced otherwise.