Parametrization in Green's theorem is often necessary for line integrals over a plane, but its use can depend on the specific problem. While sometimes re-parametrization may be required, the choice to parametrize is generally flexible and aimed at simplifying the original problem. Typically, line integrals are parameterized, while double integrals for bounded regions are not, unless dealing with non-flat surfaces in higher dimensions. Understanding when to apply parametrization can help clarify the process and improve problem-solving efficiency. Ultimately, the decision to parametrize should enhance the ease of calculation in applying Green's theorem.