So ....... there are no rules, right?
Like Bonnie, I have to understand it first, now I can just get on with it. I guess a really good use might be to enable me to play some of the really difficult chords that my old fingers won't otherwise reach. I take your point Bill (\sables) about using it as an excuse not to learn the chords but some of them really boggle my fingers!
Thanks all for great explanations.