A big benefit of using RenderGarden vs. the AE render queue is that you can run multiple render processes simultaneously, even on a single computer. If After Effects were fully multi-threaded this would not be much help, but in AE's current state RenderGarden can often double or triple rendering speeds, meanwhile leaving After Effects available for you to continue working.
Programs like Tractor have a centralized database of their various render tasks. A hack used by RenderGarden is that the filesystem itself is the database, with the priority of the various jobs controlled by their place in your drive's hierarchy, their status determined by naming conventions. This system isn't as bullet-proof as Tractor, but it's simple, cheap, and works for small-scale users and teams looking for a little render farm functionality.
