Overview
3Delight for Maya adds a few attributes in Maya's Displacement Shader nodes. The Rendering Displacements tutorial page provides in-depth explanation about these features (and more), along with illustration of their usage; a highly recommended read.
Displacement Bound
Specifies the displacement bound for the attached objects, which is the amount by which the bounding box of each object should be increased to include the displaced surfaces. Failure to provide the renderer with a decent value will result in shading artifacts (when the value is too small) or inefficiency (when the value is too large). Refer to this section for details about when you should bother to adjust this value, and how to figure that value. The default value is ‘1.0’.
Displace Vertices Only
When this attribute is turned off, a pixel level displacement is performed; the geometry is tessellated on-the-fly and adaptively. Turning on this attribute will make a vertex level displacement occur; in this case the geometry is pre-tessellated to the amount of subdivision specified in Subdivision Steps.
Both approaches have their pros and cons as shown in the table below. Lower memory usage thanks to a smart caching system. This is not always true though: in this case, 3Delight needs to keep original geometry in memory and this could be expensive in case of subdivision surfaces. Displacement quality depends on the Subdivision Steps. Note that 3Delight will use bump mapping on the final geometry faces to achieve a fine grained look. So even with low Subdivision Steps, high frequency details are preserved by varying the normal over the surface.Pixel Level Displacement Vertex Level Displacement Startup time
Fast startup time because no pre-processing is required. Potentially slower startup time because of pre-tessellation requirement. This depends on the number of Subdivision Steps. The higher the steps the slower is the pre-processing time. Overall Render Time
Slower render times. Usually faster render times. Memory Usage
Potentially higher memory usage depending on the Subdivision Steps. Although in the case of subdivision surfaces, this metod might use less memory overall because final tessellated and displaced geometry is stored as a polygonal mesh (more compact than the subdivision mesh counterpart). Quality
Provides very high quality displacement but might be subject to cracking, especially for vector displacement and large displacements.
Subdivision Steps
This specifies the number of subdivision steps to use when pre-tessellating the geometry. This attribute is ignored unless Displace Vertices Only is enabled. Raising the number of steps will increase the start-up time, raise the quality, and possibly increase the memory usage during rendering.