Activate the ambient occlusion box in the world tab but it seems to lighten the scene more instead of darkening it. I know another way is to use pass de ao and then compose but I wanted to know what ambient occlusion does in the world tab.
What is the difference between ambient occlusion in world tab and render pass with composition?
I use cycles
In modern versions of Blender (we're at 3.1.2 right now), there is no AO in the world tab of properties. So presumably, you mean using AO in the world shader, something like this:
In which case, doing that is the same as using a 1.0 white world.
Your world does not have a surface. Even if it did, its surface would be an infinitely large sphere. There is no such thing as ambient occlusion on your world, so Blender returns no occlusion-- full white.
If you want to use ambient occlusion to do something with your materials, you use ambient occlusion in those materials. Something like this:
We can see that where the cube is occluding ambient light-- occluding the world-- we're getting purple emission instead of gray emission, on the floor, whose material has its very own AO node.
In previous versions, but we're talking way back like 2.79, there was an AO option in the world. IIRC, this provided a 1.0 white world in lieu of what you specified in nodes, appropriate for baking AO. Which, yes, would almost certainly make things brighter, because most worlds are not that bright. I think there were also settings to terminate rays to AO after a certain number of bounces, meaning ignore any further geometry and just extend to hit the world, which would also make things more bright, because you had surface albedo absorbing less of the world's light.
