AO in Corona is meant only as a dirt simulation, not GI simulation, and as such, is independent on the actual lighting. You should never, ever get into a situation where you need to "enhance" the GI solution with AO in Corona.
Exactly... AO in Corona is meant to be primarily used as a tool to create procedural weathering effects and similar things. It is not meant to enhance accuracy of Global Illumination solution, as GI in Corona is very accurate. Applying AO to pictures rendered in Corona will actually ruin your picture instead of enhancing it.
Some people make mistake of creating very high albedo materials, like absolutely white walls for example, and aside from slowing down rendering a bit, it also removes most of the contact shadows, which people then try to bring back with AO. That is extremely bad approach and prime example of how things should NOT be done ;)
And that does not apply only to Corona. It applies to most of the renderers out there. These days, only renderer i can think of that has so bad GI solution it needs AO to enhance lost contact shadows is Mental Ray.
