Assuming that Jim was talking about speaking the last phrase or two -or the occasional entire verse- of a song, I'd have to disagree. It was quite common among traditional singers (in England at any rate, in the early part of the 20th century) but, when (if) their songs were published, there was usually no mention of that. If you have the opportunity of looking at the original collectors' notes you'll get a better picture.

I'm sure, though, that Jim is right in saying that it is often just an affectation nowadays; a thing that people do because they think they are supposed to (like always omitting final -g). The whole point is that a singer needs to absorb a song thoroughly, and live it. When it has become real to you, when you believe that what you are singing is really happening now, then you will know what to do with it; and your audience will take the point.