What's the purpose of a PlayerController?

From looking at the shooter example, it looks like the player controller binds input to generic things like checking leaderboards or chatting, not to movement specific input. If I have a player controller that unpossesses a ground pawn and possesses an aircraft, it would make sense for movement specific input to be bound within the classes of the actor types (AGround vs AAircraft). Am I understanding this correctly?

When a controller possesses a pawn, doesn’t it handle who is receiving input from the gamepad/keyboard? Like in my ground v. aircraft example, when I possess the aircraft and it binds all the inputs, what tells the input manager to stop sending input data to the ground unit?

Thanks.