With disadvantage, same thing as the players get to see the low rolling die 'stealing' their success. the inevitable pair of failing rolls is double-demoralizing. The other players aren't quite that bad, but they do have a variety of sarcastic responses to the same situation like 'Watch out floor, I'm coming for you!' and 'Ha! I will destroy the very air surrounding you so that you will suffocate and die. I have one player that refuses to roll damage before he has confirmed that the attack has hit because seeing that he rolled really good damage for the attack and missed frustrates him too much. I think advantage and disadvantage are fun and interesting mechanics - I hate what they do to my players though.
