Baking cakes, quick breads, cookies, and other doughs often calls for a technique called creaming. This is a method where you beat sugar and fat together to incorporate tiny air bubbles into the batter for a light, airy finished product.
Different forms of creaming will achieve different crumb structures.
For quick breads (like Banana Bread, zucchini bread, etc.), it is common to beat eggs and sugar together and then add oil. This achieves a batter that cooks into a moist heavy cake. Another method is to cream butter and sugar together and then incorporate the eggs. This is used in cake batters and achieves a lighter, spongy crumb.