All fats, whether solid or liquid, provide flavor and richness. Fat also helps with leavening, which is what helps the dough rise.
Baking with fats creates a rich tasting experience and more flavor overall. Another plus: cakes and cookies will be moister when baking with fat.
Fat creates tender baked goods by slowing down the formation of gluten. When fat coats flour it acts as a barrier between the protein and water. That’s why rich bread like brioche or cinnamon rolls are richer and more decadent in comparison to a baguette or Italian loaf, which don’t have any fat in them.
Solid fats, like butter, can help baked goods rise. When you cream butter and sugar together, it creates an aerated mixture that provides lift before, during, and after baking. Butter also contains water, and when the water evaporates, it creates flakey layers critical to a pie crust or biscuit.
Butter is considered a solid fat because it is solid at room temperature and oil is considered a liquid fat because it’s liquid at room temperature. Because of this, you can’t rely on oil to provide any leavening help in baked goods, which can result in a denser texture.
Do not substitute one for the other