You can define Parent Copy derivations to obtain parent values without cascade processing if the parent value is subsequently altered. Parent Role Names are derived from Foreign Key relationships.
For example, in the Demo application, we want to retain the quoted product price so that it does not change if the product price is subsequently ordered. This provides the intended business result: if you buy on Monday, your order total is not affected by a Tuesday price change.
Contrast this to a formula, which provides parent reference with cascade processing.
Note - this only applies during a POST - changes to the parent attribute will NOT impact this attribute on the child.