It would really be an advantage to the game. Not only seeing the performance of the own players, also seeing the performance of the opponents. In real life a trainer/manager sitting on the bench also sees both teams and all players and this gives him the chance to react.

It would be enough if the actual persormance number is on the position of the player and that number is updated every 10 min matchtime.

That would avoid situations, where you are changing a player you think is not playing strong (not mentioned in the comments) and then you read "XYZ is leaving the field after a great performance and is replaced by ZYX".