Originally Posted by DaveSSS

If I took chains out of service at .5% elongation, I'd not toss them, just put them aside. If 5 or more chains have been used and new-chain skip has never occurred, it would indicate that you're probably not using each chain long enough and wasting money on chains, just to add a little more life to the cassette. Each of those used, but not worn out chains could be used longer.

All of this depends on how costly the chains and cassettes are. Weight weenies will use $70 hollow pin chains and $350 cassettes on their sram axs 12 bikes. I ride more lowly force axs chains that cost $35 and $185 force cassettes. I have far less invested, but I still don't want to toss either chains or cassettes sooner than necessary. I'll check full length elongation, roller wear and side clearance wear with feeler gages before tossing a chain. None of these wear measurements have a value that's set in stone. I wouldn't toss a chain at .5% elongation if side clearance and roller wear were both good.