When to and when to not use Ambient Occlusion?

I wonder what is AO used for as I render my scenes without it.

In BI, it’s used a lot to simulate realism in lighting since smaller nooks and other areas are darker while larger regions are brighter. Basically adding a lightening and/or a darkening effect based on the distance between two faces anywhere in the scene.

In Cycles though, it’s not used so much for realism since it’s surpassed by true GI, so you use it more for materials than for the light (but Cycles does not have a color output for the AO node).

Now I understand

That being said the AO node is great for faking internal walls… (keep AO turned off in the world settings, just change the distance there.

I’ve heard of people using AO in Cycles for preview renders. Also one artists used it much like you would in Blender Internal. He turned down all the ray bounces and used AO to add the ambient lighting. That way he had the benefit of Cycles physically based shaders without spending all the time on raytracing the indirect lighting.

When to and when to not use Ambient Occlusion?
Use it when it gives you the look you want, don’t use it when it does not give you the look you want.

The ambient occlusion is useful for an indoor view to increase indirect sun lighting inside the building. You can also use it in an outdoor view in order to increase lighting in the dark part of your scene but it’s often less realistic.
With AO :



Without AO :

That explains it.