Great 3D graphics need shadows. If you have an object in the scene that is casting a shadow, you are off to a good start. But what about the less obvious effects of indirect light sources and ambient light? This is where ambient occlusion comes into play.
In the real world, light is coming from all around us. From the overcast sky and from reflections. This ambient light is also causing shadows or differences in illumination. For instance, corners are darker than straight walls because less ambient light reaches into them.
We speak of ambient occlusion when we simulate this effect in 3D graphics. Fusion has a powerful ambient occlusion tool in 2D.
You need to provide z and normal passes and the camera input to use it. When you can provide those, using this tool can make quite a difference for 3D Texts and any 3D scene in general.