We need to modify a property from an out-of-the-box attribute.
Some examples: (this is not a complete list)
Most of the out-of-the-box attributes are very limited in how they can be changed or customized. This is also true for out-of-the-box attributes in custom objects.
In the earlier example, it is only possible to set a "Default Value". All the other properties are read-only and they cannot be modified in any supported way.
Typical use cases are trying to enable the attribute in the Modern UX (set an "API Attribute ID") or to "Include in the Data Warehouse". If those properties are not already set/enabled in the attribute, it is not possible to modify them to enable the attribute in the Modern UX or to include it in the Data Warehouse.