This is a post by Mark Brunelli on PTC site.
Engineers have long debated the virtues of parametric versus direct modeling. Some like the freedom and flexibility of direct modeling, while others prefer the feature definition and dimension control capabilities associated with parametric systems.
What Is Parametric Modeling?
Parametric modeling is an approach to 3D CAD in which you capture design intent using features and constraints, and this allows users to automate repetitive changes, such as those found in families of product parts.