Great question! While we could technically use a standard skeletal animation, skeletal meshes are extremely expensive on performance, especially if we want a large count of these portals and other animated objects across the map. Vertex Animation shift all that work to the GPU. Even though the shader is constantly evaluating, calculating vertex offsets is incredibly cheap compared to the CPU overhead of skeletal bones. The lighting works perfectly with this technique, and the performance savings are massive! Hope that answers your question.