The VRayNURBSTessellation node is used to control the quality of the NURBS subdivision of multiple NURBS surfaces with a single node.
||Select NURBS surface|| > V-Ray Shelf > V-Ray NURBS tessellation
||Select NURBS surface|| > Create menu > V-Ray > V-Ray NURBS tessellation
Generate static geometry – When enabled, V-Ray subdivides the NURBS surface into triangles before the actual rendering has begun. This allows the building of a faster intersection structure, but takes more memory. When off, NURBS surfaces are treated as dynamic geometry, similar to Subdivision meshes, and are converted into triangles on the fly. This saves memory for other purposes, but may be slower.
Max tessellation depth – This parameter controls the maximum number of triangles that V-Ray is allowed to generate for this NURBS surface. Note that this number is proportional to the logarithm of the actual number of triangles, so you don't need very high values. Also if you want to lower the quality of the NURBS surfaces, it is better to do this by increasing the Curvature threshold parameter, rather than lowering this one.
Curvature threshold – Decrease this parameter to allow V-Ray to subdivide the NURBS surface more, for a smoother result. Increase it for faster rendering and less RAM usage, but lower quality.