Render farming is when you spread a rendering task across multiple computers.
Typically this is done when multiple images are required, or for animations (including walkthroughs). Obviously rendering in parallel on multiple machines will speed up the process.
Revit doesn't have a rendering client like 3D Studio Max for render farming, but it doesn't really need it.
Because multiple computers can open and work on the same file, those multiple computers can use the same views and render settings.
One approach which typically works well is to divide up the frame range of a walkthrough. This allows a rendered walkthrough to divide up the rendering process between multiple workstations .
For example say you have a 200 frame rendered walkthrough. And you have 5 workstations which can be used for rendering.
In a walkthrough view, when you export the walkthrough under R > Export > Images and Animations > Walkthrough, you have an option for Frame Range:
If you have multiple workstations, open a copy of the project file on each workstation. Then export a different frame range on each workstation.
For example:
Workstation 1 = 1-40
Workstation 2 = 41-80
Workstation 3 = 81-120
Workstation 4 = 121-160
Workstation 5 = 161-200
This will finish the walkthrough 5 times faster, and give you 5 video files.
The last step would be to combine the video files, in an application such as Windows Movie Maker, and export 1 complete rendering animation.
You could also choose image files instead of the .AVI format. This would create still images for each frame, and they could be combined in a similar program.
It is important to clear the Windows temp folder prior to starting Revit and the rendering process on each workstation.
The default folder location is as follows:
Windows Vista\7: %USERPROFILE%\AppData\Local\Temp