This is a vote to kick by unanimous agreement of all 3 other players and is invaluable for groups who find themselves joined with a fake tank/healer who runs ahead with no reguard whatsoever for the state of the group left behind. I actively encourage people to wait until the last boss before initiating the vote* while i tidy up adds, teach and carry those remaining together.
Honestly, in normals it makes little difference if the tank is fake aslong as they - at minimum- look at the group they are with and act accordingly. Completing a normal dungeon solo is easy for higher end players butt a low lvl will find the experiance of having the adds scattered and running around messily because someone has run through ahead very confusing and deadly.
It may on rare occasions be used to troll; this is, however, highly unlikely imo.
Considering how broken the group finder is when you do manage to get into one with all players actually ported in it should be played with proper respect to everyone there.

*No one's time can be so valuable that they can justify their selfishness when they are just spending that time playing a game and kicking them at the last boss wastes thiers instead of everyone elses. Even if it is completed in record time the low lvls left behind learn nothing about the dungeon or how to play in a group... you are actively lowering the already general incompetancy of pugs by completing it for them in this way.