SFB – That’s not the theory I was lambasting.
Because chain wear is not linear – a longer chain wears the cassette much quicker than a correct length chain. So 3 chains used for a short period of time each will wear less than 1 chain used for 3 times the length. Otherwise we’d just use chains until they snapped and not worry about buying a new chain with a new cassette.
OK maybe you get something for nothing but not 3 x the life of the cassette. The cassette wears too and as you use chains that are more worn than it is, it wears them more quickly. It just seems too much hassle to me but then I CBA spending the money on light/expensive cassettes, it’s cheaper to save weight elsewhere.