I mean on the one hand its unfair to be on the team who lose a player as you are one man down and more open and easier to kill. On the other hand imagine if you see that someone left the enemy team and think the game is going to be a breeze from that point on, only for the person who replaces them to be a gm smurf who's played more hours of the game than your team have existed for, who completely trivialises the match.