I think there is a continuous wear caused by stretching a chain.

So, it isn't that everything is just fine up until 0.5%, or 0.8%, then all hell breaks loose.

Rather, a new cassette should work best with 0% chain wear, and will start seeing the chain climbing on the sprockets as one starts getting chain wear, and thus damaging the cassette.

So, extending that period of time just makes sense to me.

The question then is whether one is better off say rotating chains.

Riding to say 0.1% wear. Pulling it, putting a new chain on, riding it to 0.1% wear, then putting the original back on and riding it to 0.2% wear before rotating again.

That would be a lot of rotating, but a good opportunity for cleaning and maintenance.

And, of course, I hate putting a partly worn chain back onto my good cassettes and chainrings.

I do distribute my riding between a couple of bikes, but I do get quite a few miles in a year, so I can chew through quite a few chains & etc.

What I'll probably do is keep good chains on the road bike, then rotate them onto the commuter. Perhaps I can even break the sprockets into say a 0.3% worn chain.

As far as chain value:

Say Chain X costs $25
And Chain Y costs $50, but gets 2x the wear of chain X. Then I believe Chain Y may be a better deal due to making the chain wear through the least damaging periods longer. If, however, Chain Y gets 3x the wear, then it should be the obvious choice.

As stated, I'm still early in the Wippermann testing, but I have high hopes.