When performing certain shader tricks using RenderTextures or for certain kinds of games and interactivity, Culling Masks are really useful as it means you can selectively render certain kinds of objects without disabling them and with it any other functionality they have.

VRChat currently doesn't support this with the Main Camera - any Culling Mask options selected are not inherited by the final camera that players see from and there's no way to set the Camera's Culling Mask using Udon.

The current workaround solution of using OnPreCull() and OnPostRender() to manually enable and disable every object you need isn't flexible and is presumably much worse for performance than just using the tools Unity already provides as you're having to iterate over potentially dozens of objects at least twice per frame.