Nurbs
In CAD 3D Design, NURBS (Non Uniform Rational B-Splines) curves and surfaces allow rapid and global modeling. They are mainly used in the exploration of aesthetic form, most often in the upstream stages of a project.
Due to their multi-segmented structure, the intrinsic continuities cannot be managed from one segment to another. This makes it difficult to apply in the details of shapes.
Bézier
Most of the time, bezier curves are the step that allows you to go deeper into the details of a shape. Indeed the fact of having several mono-segmented curves / surfaces makes it possible to locally manage the continuities in Tangent / Curvature / Torsion.
Bézier curves are used as the quality of the shape to be achieved increases, Class-A type surfaces.
