The matchup ratings gives you and idea about how effective -in order to make points- could be a position in a determined game. So, they change from game to game even if the games are played with the same players.
Because there are probabilities the actual performance is related to the Matchup Ratings but is not the same.
They would help you to learn how your team works when played a against a determined team. For example, if youre using netrual ofensive tactics and you see that in every game your AP and P are getting 156, maybe, it will be better for you to try and Inner Focus in offensive game. There are several things you might learn, all of them related to the ability displayed by a certain position to make points. A more broadly view of your players contribution would be to compare your team califications. And a more broadly view of the performance of a specific player would be his Rating.
Sorry about my english.