Something magical happens when you cook watermelon. It has a delicate flavour and a high water content so cooking the fruit before making the cobbler helps to intensify the flavour and release some of the water. It also changes the consistency to something similar to a peach. And it gets really sweet. So by reducing the sugar in the cobbler batter it helps to balance the sweetness.
And, with Halloween approaching, cutting up a big melon is good practice for your jack-o-lantern carving skills!