I'd say that it depends. For shorter chains (20" and under), if you're using good chain and it's broke in, you should be able to go 4 or 5 tanks without needing to adjust the tension on the chain. If you're running a 28" or 32", you'll probably need to adjust it every 2 or 3 tanks. If' you're running something that's 36" or more, it's worth checking on every tank. That's the way it has worked for me, and I cut mostly hickory and oak with some locust thrown in.What a stupid closed minded blanket statement to say.
It's a big world out there not everyone cuts rolled up foam mattress. Needing to adjust the chain at every tank refill and giving the chain a rub is the norm cutting hardwoods around my part of the world.
Almost as bad as the clowns that say you can get days out of a chain before it needs sharpening or ya doing something wrong! What a small sheltered world some guys live in they think what they do applies to the world