Games : What's XP for past level 20?

In Top Spin 4, XP is used to level up. Once you reach level 20, though, you have supposedly reached your peek performance and can only change your stats by hiring a different coach. How well one performs beyond that is all up to the player.

And yet, the character keeps gaining XP after every match and the game keeps saving this change (though it might save other things for achievements and such).

Is there a purpose to the extra XP accumulating? Some achievement perhaps?

This is on PS3, in case this would make a difference.