It's not about the rest aspect per se, it's more of a precautionary measure to ensure your key players aren't injured for the (arguably) more important games.
For example, you wouldn't enter your prize marrow in the fruit and vegetable competition at the local village fete a few days before the National Giant Vegetable Championship....
http://www.guinnessworldrecords.com/news/uk-gears-up-for-national-giant-vegetables-championship/