Originally Posted by
Barrettscv
A multi-speed bicycle chain has extra clearance built into the uniquely constructed pins and bushings and large clearance between the link plates. The sideplates don't bend, the clearance allows for side flex. I'm not suggesting that a cyclist should stay on the cross chaining combinations for miles at a time. I'm just saying that no damage or unusual wear will result from crosschaining.
Just to clarify here, modern bicycle chains are bushingless.
According to the treatise on Sheldon Brown's website on this, the reason for the flexibility in modern derailleur chains is because of this lack of bushings -- that is, the bevels on the shoulders on the inside of the outer plates provide that flex, something which the bushing-ed chain would not be so capable of doing.
And it might be worth going further -- one of the reasons why chains do tend to wear and become sloppier in their sideways flex is because the shoulders on those outer links are more prone to wear than the older style bushing-ed chain.