There are steps to every baking recipe and each one is linked in sequence to other steps. It’s important to follow them.
When a cake recipe asks you to beat sugar until it’s fluffy, we aren’t trying to be romantic, it’s an important step, the most important one in my eyes. By beating the sugar and butter or egg for a good 5 minutes at the beginning of your mixing process, you’re breaking the fats in the butter up, which means the cake will bake more evenly. You’re also emulsifying the fats and beating air into them; this will make for a lighter and fluffier cake. The beaten butter should resemble a thick mayonnaise after you’ve beaten it properly.