You usually can get a wider range of gearing with more possible combinations on a 3x. However you won't find a high tier 3x for 11 or more speed rears.

You might find the range you need on a 2x bike, but you also might loose some in between ratios that let you hold a particular speed comfortably when riding with others.

At least that's what I get out of it. I've never needed a 3x. But I'm not carrying loaded panniers and riding through gravel either.