What is the difference in outcome in baking cookies, if you use butter in different aggregate phases?

The softer the butter, the more they will spread when being baked.

Sometimes, cold butter is essential for a more crumbly end result. Shortcake, crumble topping, pie crust.

As mentioned above, butter temperature is critical when baking. You can use the same recipe and get wildly different results based on the temperature of the butter. Try making chocolate chip cookies with melted (or almost melted) butter and watch them spread into thin crisps as they bake.

And yes – pie crust demands ice cold butter.