Especially when using Team Render, having an un-cached Global Illumination (GI) or Ambient Occlusion (AO) effect can drastically slow down the preparation time of your render as your machine(s) will have to calculate a "prepass" to render these effects.
If you're using Team Render, it's also important to understand that different machines do not always calculate random seeded effects like MoGraph, Dynamics, GI, AO, etc. the same way as your main workstation, so it may actually be necessary to cache these effects to create a uniform look in the render.
To remedy these problems, it is recommended that when you are ready to render and have no further edits to make in your project, you create a GI or AO prepass cache so that your machine(s) can quickly reference the cache rather than having to calculate the prepass before each render. These prepass cache files can also be shared by your Team Render Clients if you're using it, so it allows your render farm to reference a prepass that uses data from your workstation instead of having to calculate the effect itself and create a different looking effect (this is what causes flickering or checkering in the render).
Before creating a prepass cache it is recommended that you first do a File > Save Project With Assets. This will create a project folder where the project and all of its assets are self contained and easy for the program and any Team Render Clients to reference them; this include the GI and AO cache files, as well as external textures, dynamics or MoGraph caches, etc.
There are different methods for both GI and AO, but they are each very similar:
- To cache Global Illumination, just go into your GI settings under Cache Files and make sure that "Auto Save" and "Full Animation Mode" are turned on, then enable "Prepass Only" and start the render using only your local machine (do not Team Render). When this is finished, go back to your GI settings and disable "Prepass Only" and "Auto Save" and enable "Auto Load" and "Skip Prepass (if Present) and start your render, or Team Render.
- To cache Ambient Occlusion, the process is very similar. In your AO settings, make sure that "Auto Save" and "Full Animation Mode" are turned on. You'll notice, however that there's no option to do a "Prepass Only" like with GI. Instead, enable the "Material Override" setting and run your render. This will make your project render with just the default grey material and should allow the render to complete faster than it does with them all enabled. Once you've done this, disable Material Override and in the AO settings enable Auto Load and disable Auto Save, then run your Render/Team Render to use the new prepass.