Originally Posted by carpediemracing

There was a story about how Shimano had to increase durability of chains when they first came out with the hardened pin chains (for index shifting). Some pros like Phil Anderson were going through a chain in two weeks or less.

However I don't think it's about wear. It's about (probably) the perceived extra friction. In a pinch it may not matter, like I found myself in the big-big Sunday by accident (group ride, not a race, and I was already dropped). I quickly changed to a similar gear using the small ring.

It's also about risk. Someone on that ride lost their derailleur when it went into the spokes. Big-big means your derailleur is under all sorts of tension - derailleur maxed out to the inside against the in-out sprint, cage pulled taut maxing out the pulley cage spring, and derailleur pulling chain hard from the outside. You lose all your margins of error - slightly loose dropout, slight misadjustment, slight spoke looseness, etc. The small-middle equivalent offers much less risk. If you back pedal in the small-middle probably nothing will happen. In the big-big you'll realistically derail your chain.