Generally they will just wear your new chain quicker if using on a part worn cassette, its not advised. Try to balance the cassettes with similar mileage.Martin I agree, if you let everything go on until it's all knackered you'll get more miles.
So this way of thinking is a culture shock.
As I'm running two cassettes with different ratios, keeping on top of the chain makes sense, at least it did when my bikes had full sized front rings, now I'm not so sure.
As to expensive chains, will they bring my worn sprocket back to life or make a new sprocket last longer.
You'll be please to know the sprockets are half the size and therefore half the price of a conventional alloy ring
Martin