It's an extra scrimmage for teams out of playoffs. The purpose of the match is to give your players some extra minutes.
and to clarify a little more:
you can set training for your players and the players actually need to have played during the week to be able to get any training, so by having the extra game, you can have the players who played in the game some extra training...
I sugest you read the rules about training first, then, if you ant to know a little more on the details, read about it in the help forum, there is tons of info about the subject. Should you have any questions left, go ahead and ask them.
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