I've used campden and not campden and can't tell any difference. I understand that chlorine 'gas' will come out of the water quickly when heated. My city water department uses chlorine 'gas', I called them and asked. So apparently, campden is good where chloramine is used but probably a waste of time and money where chlorine 'gas' is used. But I guess I'll use up what I have left anyway and probably not bother with it any more.
"Doubt is not a pleasant mental state, but certainty is a ridiculous one." - Voltaire