Answering my own question here. A CVAR value is a setting value, so zero is not just a null value. For example, As with the anti-aliasing values, the console variables used here focus on quality over performance.
For Ray Tracing Global Illumination (r.RayTracing.GlobalIllumination), setting a value of 1 calls the brute force method. This is accurate, and allows multiple bounces of indirect lighting, but is computationally expensive. If you were to change this value to 2, it would use a temporal history method, which is much faster but only allows a single bounce of indirect light, and produces some ghosting artifacts (pixels that trail after a moving image).
The other CVARs in this exercise use scalable values that control the quality level.
If you want to know the details of a console variable, you can use the backtick ( ` ) key to open the console and search for that console command. Use the following format to display the tooltip:
[consolevariablename] ?
For example, if you input r.RayTracing.GlobalIllumination ?, the output of the tooltip would look something like:
HELP for 'r.RayTracing.GlobalIllumination':
-1: Value driven by post process volume (default)
0: ray tracing global illumination off
1: ray tracing global illumination brute force method enabled
2: ray tracing global illumination final gather method enabled