I agree that according to my understanding of the gift of tongues is that it is speaking in actual languages known to people on the earth. I think that it would have some useful purpose. Such as if you are able to talk to and/or understand someone who doesn't speak your language, or to read or translate something written in another language. Even learning another language relatively easily could involve the gift of tongues.

I have heard people say some interesting things and/or make interesting noises in their sleep though. I don't think it's the same thing, in most cases.