Rifleman, I really can't see how your last comment contributes to the discussion. The initial question was, "What are the pros and cons? Should they be introduced, how, to what extent, why, in what circumstances?" You have not answered that.

Don't know why, but I posted to this thread when I got home from a most enjoyable evening listening to Jackie Oates and James Dumbleton, but now my post has disappeared. What's worse, now I can't remember what I said! But things have moved on now anyway, so not to worry.

Thanks, all of you, for your contributions, and more, for the manner in which you've made them!

Barbara x