Many of the settings in the Advanced Tab you will never need to edit.  However, for the more advanced user who wants fine tuned control over RenderMan for Maya, they are here.

Render Options

Enable Object Instancing: Instanced Maya DAGs will be emitted as object instances, providing significant speed and memory benefits.

Procedural Reentrant: This allows procedurals to run simultaneously in multiple threads and greatly speed up renders with procedurals (hair). You most likely want to leave this on.

Output Shadow AOV: When using the Holdout workflow, output the Shadow AOV

Enable Image Plane Filter: Render the image plane using the Pixar Image Plane Filter (Maya uses an actual geometric plane)

Adapt All: Apply the sampling quality criteria (pixel variance) to all color/illumination AOVs. This can increase render time as some AOVs may have more noise than the Beauty and trigger more samples through all the AOVs.

Adaptive Sampler: Make use of the improve sampling algorithms instead of the default. You may need to slightly increase your Pixel Variance setting to avoid longer render times (but better resulting quality on complex images)

Bucket Order: RenderMan subdivides the output image into small rectangular regions called buckets, and renders a single bucket at a time. This allows a small portion of the image to be in memory at any one time. The drop-down list allows users to choose the order in which buckets are displayed in "it" or the Render View. The default is Spiral. Note that only some bucket orders are supported for checkpointing and recovery.

Bucket Size: Specify the size of the buckets. Larger buckets will require more memory to render. Conversely, smaller buckets are less efficient for shading, but will use less memory during rendering. If your scene is using a lot of memory, you may want to try setting this field down to 8 by 8 or even 4 by 4 buckets, but most likely you will not change this.

Opacity Threshold: Controls the Opacity Threshold, if set too low, it may terminate rays early on semi-opaque objects. An objects opacity is controlled by the material Presence parameter.

Reference Frame: Once per job passes and static objects are evaluated at the frame designated here.

Dicing

Micropolygon Lenth: Controls the tessellation rate for displacement.  The default setting of 1 will dice displacements to 1 pixel's size.  (As seen from the dicing camera, typically the render camera).

Watertight Dicing: Closes pinholes in diced geometry or attempts to close gaps in displacement.

Dicing Camera: Enables the use of a reference camera for dicing. This can be done globally, or restricted to specific objects (e.g. objects with displacements that "sparkle" as the camera moves) by also attaching this as a per-object attribute.

Reference Camera: Specify the camera to be used as your dicing camera here. Click on the widget to create a new camera, or right click in the field to select an existing camera. Note that the Reference Camera needs to be different from the render camera.

Hair

Min Hair Width: Sets a minimum width for hairs/RiCurves. Narrower hairs will be clamped to this value and their opacity will be reduced to compensate for the difference in visual weight.

Trace

Trace Auto Bias and Trace Bias: RenderMan will automatically compute a trace bias for displacing ray origins off a hit surface.  However, if you wish to turn off the auto bias, you can set the bias manually here. Per-object settings should have Auto Bias turned off.

Trace World Origin:

Crop Window

Specify the coordinates for a crop window to render. This can be useful when rendering many iterations for debugging or lookdev when only a specific region is under consideration.

IES Lights

While scenes are exported to rib "unitless", IES files specify a unit measure.  Use this setting to specify the scene unit to meter conversion factor.  For instance, if 1 unit = 1 meter, use 1.  If 1 unit = 1cm use 100.

Cleanup

Select the types of files that will be cleaned up on a per-job and/or per-frame basis.

RIB Options

Allows users to choose between ascii and binary RIB output (binary rib is smaller and faster but ASCII is readable), whether or not to apply gzip compression, the number of places past the decimal for floating point numbers in RIB, and whether or not RIB is generated "lazily", with full paths, or flattened.

Ri Injection Points

Provides Ri entry points for inserting MEL scripts which will be run during ribgen.

Ri Filters

Provides an interface for enabling, inserting, and arranging RIFilters.

Default Shading

Allows users to specify a global default custom shading group (as opposed to per-pass shading groups specified via the Passes tab).

Cache Sizes

Allows users to customize the cache sizes for various assets, including textures, Deep Shadow files, brick maps, ray-traced geometry (specifically the tessellation cache), and procedurals. The values are in kilobytes, and the renderer will automatically unload data from the cache when the limits specified here are reached.

Statistics

Enable this to output diagnostic information from render jobs. Useful for timing, debugging, and seeing what RenderMan is doing. You can specify a target destination for both "Old School" and XML statistics.