What effect do advantage and disadvantage actually have in D&D 5th edition?
While the average implies that advantage doesn't make a huge difference, in practice, you're going to see much better rolls. It's highly weighted towards high numbers, which means you'll be rolling almost twice as many critical hits, and critical misses become extremely unlikely, at only one in 400.
When analyzing average damage, you have to take critical hits into account. Let's try it with a 2d6 weapon and a strength bonus of +5, which does x2 crit on a 20.
How about a 1d8 weapon with x3?
Advantage doesn't make a big difference when your enemy is easy to hit, but against hard to hit enemies. Against average enemies, you'll be doing more than 3 times as much damage with advantage as with disadvantage, and with really tough enemies (16 to hit), you'll be doing almost 8x as much!