Yes, I have used AO inside C4D. It is faster but not by much if you have higher settings (which makes a better picture). It can also add some erroneous effects if applied at a scene level. Usually best if used in individual materials but more work required.
One other thing is that AO does not take into account radiosity and can create some lighting errors in that regard. It is a useful tool but one to be used with care.

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