The following will help you optimize render trees, as well as troubleshoot common problems with them.
When working with several shaders at once, it may be best to turn off the auto-refresh option for the render regions. This prevents the render regions from updating every time you make a change to the render tree.
To turn off the auto-refresh feature, choose Render 
Regions Auto-Refresh from the Render toolbar.
When auto-refresh is off, you can manually force the render regions to refresh by choosing Render Regions Refresh or by pressing F5 while the mouse is over a viewport.
To see how a particular node affects the render tree, connect it directly to the Material node's surface input. When you're finished previewing, reconnect whichever node was originally connected to the surface input.
Replacing an Image Clip with a Texture Shader
Make sure to connect the State Vector shader to the Coordinates input of a texture generator shader when it is being connected to an image shader.
For example, if you have an image shader with an image clip connected to an object's Surface or Bump input and you wish to replace the image clip with a Clouds texture, connect the Clouds shader to the input of the image shader. Then connect the State Vector shader to the Coordinates input of the Clouds shader. This gives the clouds a set of vector coordinates.
If you like complete control of all your textures, you can connect a Color Correction shader after (to the right) of each texture shader or any shader that outputs a color (RGB) value. This shader lets you control the Gamma, Contrast, Hue, and Saturation of a color value.
Number of Shaders (Speed Optimization)
Try to use as few shaders as you can while maintaining the look you want. Softimage may slow down if an excessive number of shaders is used to create an effect.
You may find that a single shader can replace two or three shaders that are made redundant by options available in the one. This may often be the case with surface shaders and texture shaders that have built-in alpha controls and don't require any of the alpha conversion shaders.
