I think someone previously made a distinction between the two (maybe Teacherman?). I think the distinction was in connection with full x-t vs. less-than-full x-t.
I hope whoever it was might rearticulate their view, as I have reason to believe it might be a topic worth discussing. I say this knowing or thinking that at the time I myself was scoffing at the notion. But I would like to hear the idea once more.