For what its worth the bike industry has realized people love cross chaining, so most current high end 2x setups are designed to cross chain pretty well. In funny contrast, DI2 won't allow some small/small combinations (depending on configuration). There is a drop in efficiency and a bit more wear, but you certainly can cross chain for short moments. I'm a pro mechanic and I'll admit I ride in my big/big on my road bike for short moments sometimes out of stoplights and occasionally when cresting a small grade reversal or something to avoid an awkwardly timed front shift. It's not a huge deal.