Some of the advanced tessellation parameters can dramatically increase rendering times.
Because the tessellation of NURBS surfaces has nothing to do with the material assigned to the surface (unless the surface is displacement mapped), you can start adjusting tessellation early in the process, anytime after the object is modeled.
To adjust tessellation on NURBS objects
If you want to apply settings to All surfaces, skip this step.
(You can also adjust some of the Automatic tessellation settings to optimize the default settings. See Automatic Mode settings.)
Always start with the Basic settings. Basic lets you adjust a smaller number of settings that automatically determine some of the more advanced settings.
Some of the advanced tessellation parameters can dramatically increase rendering times, so choose them wisely.
Fine-tune the adjustments you’ve just set until you reach an adequate level of smoothness.
To prevent overtessellation of objects, use the Use Smooth Edge attribute in the Render > Set NURBS Tessellation window to increase tessellation only along the edge of the object.