Chilling cookie dough is an important step to develop the flavors of the cookie. The flavors meld together, the dry ingredients absorb the butter and sugar, and the cookies become richer and more decadent. So if time is on your side, chill the dough for at least 24 hours! Chilling the dough for 24-48 hours helps the ingredients to incorporate. The gluten which is developed by mixing the dough, is relaxed while the dough rests, which creates a more tender cookie. The moisture in the dough is absorbed by the dry ingredients, which helps to dissolve the sugar, and causes extra caramelization. You end up with a chocolate chip cookie with rich toffee notes, a chewier texture in the center, and buttery, crispy edges.