Ambient vs Indirect Intensity

What’s the difference between Ambient and Indirect Intensity, or do they essentially do the same thing?

For a ‘natural’ sunlit scene, should you keep your Ambient Intensity set to zero?

The tooltips in the Editor explains this in detail. As far as I remember, Ambient Intensity is light from the sky. Indirect Intensity is a global scale on the bounce lighting, ambient and emissive.