Vertex normals are used in Gouraud shading, Phong shading and other lighting models. Using vertex normals, much smoother shading than flat shading can be achieved; however, without some modifications to topology such a support loops, it cannot produce a sharper edge.
Vertex normals play a crucial role in achieving smooth shading effects, especially in methods like Gouraud and Phong shading. However, their effectiveness is limited by the need for supporting loops or other modifications to the mesh's structure to create sharper edges.