I have no problem using any of the cassette's gears with my smallest of 3 chain rings should the need arise. But I do avoid it for extended periods. I don't normally use the small chain ring anyway, So the few times I use it isn't a problem.
I too think you can safely use the big - big and small - small gears in pinch. When I got my bike I avoided those combo's, But later I tried out the small - small combo. Despite cross chaining, I feel comfortable using it from time to time. The big - big combo just seems more stressed, Perhaps because the chain is so tight now, So I do avoid that combo.
Last edited by xroadcharlie; 05-25-20 at 07:13 PM.