Why is the grade of the players also used as input to models?

[shinkuan]

Wiki says that the 1st Field: Sparse Features is also used as input to model, this field contains room, grade of the players, rank of the players.

Just a simple question, why grade of the players is used? Also room and rank of the players.
Grade of the player does not affect the gameplay. What's the point of it? What is the benefit of putting grade in inputs?