What the node of set render with custom depth is used for?
I haven’t used it extensively, but I have used it before to get certain rendering effects, like outlines around meshes. If I understand correctly, it’s meant to give your mesh a modified depth rendering. If you’re not using any rendering effects or specific camera tricks, it won’t do anything for you. You have to tell it explicitly in the shader what the custom depth will look like or it will render the default depth pass.
That enables post process materials. On that object.