Some addendum:

I've given up on using AO a long time ago as I simply don't like its "look". Reminds me when back in the 80's it was en vogue to give scale models a simple "wash" of highly thinned black or dark brown paint to add "depth" and "realism". It does work to a certain extent, but it is easily overdone and then looks fake.

I think it just doesn't work well with the "normal" shadows and it takes too much time to be set up properly. (= per material)

In any case, I never was happy with the results I've got.

The deeper "corner" shadows of IDL are of course also a result of bouncing light. Less light bouncing around in dark corners/tight spaces = deeper shadows.

But unlike the AO the "IDL-shadows" blend much better with the regular shadows.

I'm not saying every render needs IDL. On the contrary: 90% of my renders are made without it.

I'm just saying I haven't found a better (faster) method yet to give me similar results.

At least not in "fully furnished" realistic scenes.