I'm interested in looking at average damage comparisons for when it does max damage for taking disadvantage. What is the probability of hitting with disadvantage compared to the probability of critting without disadvantage?
Math: let's say you hit with probability p, and roll a dX. With no disadvantage you need to hit once and get average damage, with disadvantage you need to hit twice, but get max damage. To break even you need
p*p*X >= p*(1+X)/2 or
p >= 1/2 + 1/2X
As has been noted, the flat bonuses make a big difference and tend to make rage worthless.Hm, quick calculation time:
If you hit on a 10+, disadvantage takes you from 55% hit to 30.25% hit.
An ordinary sword attack goes from 1d8+3 (average 7.5) to 11 damage. That's 4.125 vs. 3.3275.
A bigger attack goes from 1d12+3 (average 9.5) to 15 damage. That's 5.225 vs. 4.5375.
An awesome fighter attack goes from 1d12+3+1d6 (average 13) to 21 damage. That's 7.15 vs. 6.3525.
It only breaks even when you hit on lower numbers, or if you're drunk I suppose.
I want to play a drunk battlerager now...
+2d6 damage and 1d6 dr and disadvantage
Actually this is a pretty nice use for it... Anytime you're attacking an invisible enemy, or a fey warlock, or are drunk or blind or have disadvantage for whatever other reason, might as well go crazy and add a few d6 of rage damage, since disadvantage doesn't stack!

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.