You need to know what influences the player's rating, but it can be helpful. If you have a great player in terms of skills and gameshape but he gets a low rating, you could conclude "hey maybe his stamina is not high enough for the 45 minutes he played". Then you can train stamina to make the player perform better in more minutes, or get a better backup so he doesn't need to play that many minutes. Other factors can be gameshape, or position played. Maybe you have a PF or SG that you want to play at SF, then if his player rating is 3 points lower at SF than at his natural position it might not be a wise choice to play him at SF.