Depends on the cost of the cassette. I run XT cassette at the moment and £30ish a time it’s a no brainer to just let it run on.
My experience is I’ve done both methods and I’ve ended up replacing the cassette no sooner by running one chain, and in fact seems to last longer with worn chain and cassette, with no shifting issues or skipping.
Personally I was wasting money on chains and binning perfectly good chains and cassettes.
But if you don’t like the idea of riding something “worn”, even just partly, then replace early.
dirtydog – Member
Recently took to running two chains on my bikes, one wet one and on dry and swap according to conditions. Easier than degreasing a wet chain and applying dry lube and vice versa.
Or just use dry in all conditions 😉 . Wet just wrecks everything unless you’re talking road and there’s very little crud to suck into the wet lube. Plus on the road it’s maybe more useful as there’s a lot more water spray. Dry is fine all year round off road. Better still, decent wax lube like Squirt.