I think someone else nailed it - if you're riding at the edge of your capability (e.g., just barely holding on a pace line), you can have issues with a wide-range/big-gap cassette that hurt your ability to hold a fixed speed. If you're by yourself or not racing, you typically just ride a bit slower, but if you're racing or riding in a group, this may have negative consequences. I ride 1x on my primary road bike, and I honestly have never has any issues with the gaps (or the fact my top speed is slightly curtailed), but I don't race and don't ride very often in groups. And I love single-lever shifting so the tradeoff to me is heavily in favor of 1x.

- Mark