With a render farm, you send all your files to an external service, they render it for you and then send those renders back to you. With Render Boss, you basically create your render farm in your own local network.
However, you don’t need to buy fancy new computers to speed up your own farm. You can mix and match older machines, as long as they can run After Effects. Any older workstation can help with a few frames, speeding up your render. Plus, Adobe doesn’t require additional licenses for extra render machines.
(third party plugins might have different license terms)
Advantages and Disadvantages
The main advantage of using an external render farm is that your computers are not used for rendering, and those services usually have dozens to hundreds of computers connected. So the render itself will probably be faster, with a little caveat..
The caveat, and main disadvantage (other than having to pay for each render) is that you have to prep and transfer all your media, assets, etc to the farm service so they can render it for you. Which, depending on the project, might end up adding much more time than it would have taken to render locally.
Render farms are usually a perfect fit for 3D renders from applications like Maya, 3dsmax, Blender, etc. Because they take a lot of computational resources, and usually only need to transfer textures, project files, etc. Which are much smaller than video files. However, After Effects projects tend to have GBs of files and take less computational power, so it’s usually not the best solution.
With Render Boss on the other hand, all your files are already in your local network, so no need to transfer them over the internet. They start rendering immediately with a single button inside After Effects.
Render Boss makes it really easy to make your unused computers available to render, and if somebody needs to use a particular machine, he/she can stop the render on that machine, and the other machines keep going.