In many baking recipes, you'll often see that the ingredients are listed at "room temperature." This is because, when left at room temperature, things like eggs, butter, and other dairy ingredients form an emulsion that will actually trap air. That trapped air grows, pushing the baked good out up and makes things nice and fluffy. Which is what we want. So, this is also why I like to recommend setting out the ingredients the night before you plan to bake the rolls, so the ingredients have the chance to really get to room temp.