Yeah most of the multi-boxing afkers are a drag on the team (take up 3-5 slots on the team), but a few of them have been good/contributed
In BFA there was a multi-boxing Boomkin player with x5 Druids in the same bg. He was good though, he properly used the raid leader warnings to herd the pugs into the correct strat (telling them to go hangar, etc)
Then there was that one Unholy DK multi-boxer that brought his x23 Unholy DKs into the same instance. He would single-handedly win teamfights with his mass AOE spam and carry the Alliance pugs all by himself.
Just like the afker ones though, all of these guys “suddenly” disappeared/stopped queuing as soon as they hit honor level 500 and unlocked their horsey mount 