The only time you should ever use a knockback in a group is if you get aggro and the tank can't get it off of you. In other words, an emergency.....period. It is an annoyance to tanks and melee dps, for more than 1 reason. You make them have to run around to get back to the target to continue killing it, for one. It also screws up their rotations.
If someone in my group is continually using a knockback just because "they can" then I will ask them to stop. If they keep doing it I will ask them a 2nd time to "STOP please!" If they continue to do it I won't ask a 3rd time and you will be vote kicked....sorry. Knocking mobs back because "you can" is not getting through dungeons, or any other content efficiently. Save it for solo play.
