Hi.Blender users.
I have a few questions about Ambient Occlusion Node (AO node) in Shader Material.
I understand that Ambient Occlusion is the darkest part of shadow.
Ambient Light (= Indirect light) cannnot reach to the area.
Without using AO node, I can see Ambient Occlusion in cycles render,
and the result looks realistic to me.
Ambient occlusion is an old trick from before global illumination / path tracing. Before we could get all these subtle shadow & bounce interactions for free, back when surfaces were simply lit or not lit (think classic CG—Blender Internal, bowling alley screens, 1990s SIGGRAPH demos, etc.), that simple trick, darkening faces that were close to each other, was a great way to fake some of that more complex behavior, help objects feel less like they were floating, and make our renders look better.
And yes, as you’ve correctly noted in your Cycles render, what we used to fake with ambient occlusion happens automatically now: it’s no longer necessary (assuming you’re using a path tracer. Real-time rasterization engines, like Eevee or games, still need to lean on all those old tricks). The Ambient Occlusion node in the shader editor is there not because we need it to fake shading interactions anymore, but to help you build other shading effects that might benefit from a black-and white mask of crevices / contact points: think dust collecting in grooves, moss growing at the base of objects, etc—or to just go wild with stylized shading effects.
