This is referring to primal battles and the like, not full dungeons.

The following happened to me personally in the level 49 boss, and I don't think it's fair:

I am WHM. I got in, discussed strategy with my party members, and casted protect/stoneskin on all. Within seconds of the fight actually beginning, my internet lost connection, as it's prone to do. It was down for a few minutes, in which I went to take care of a few things around the house. When I came back, fully prepared to have to requeue for the fight, I logged in instead to the tone of victory music. Even though I didn't do anything at all during the battle, I still got quest credit and exp, which I don't think at all is fair, as I was not there for 95% of the fight.

Granted, if someone disconnects with the boss at 10% HP, yes, they should get credit if the party manages to beat it. But in this case, I feel as if I cheated. :-(