okay, ran a bunch of tests again.

Let's summarize, from the original question on. What's the net effect of (additional) raytrace bounces, is the pain worth the gain?

We've got two areas of concern: IDL and raytracing (reflection/refraction/fresnel).

First: IDL. When bounces go up, lighting levels go up and to some extent, dark splotches in problematic areas, especially right corners at wall/ceiling joints and the like, will get reduced.
As every value for bounces introcudes it's own balance of the IDL with non-IDL lighting effects (ambient glow, specularity, direct light and shadows thereof, ...), every change of value will only affect the artefacts but will also distort that balance.

In order to handle ID bounces separate from raytrace bounces, one has to use the (Scripts > Partners > Dimension 3D > ) Render Firefly route instead. On top of that, one can enter any value in the value-box, while all sliders (and the value box in the regular Render Settings) max to 12.

Larger values make longer rendertimes, as far as the IDL rays bounce around indeed.

Second: raytrace, and for the sake of it: without transparency (T=0 or white) for the moment. Actually, these processes are quite efficient. Each surface affected takes one bounce, so reflections take one per object and refractions take two. Refraction caters for the 100% transparency itself. As the value is a max one, Poser only takes what's required and higher settings do not present larger render time.

So, for reflections of reflections of ... as well as refractions of refractions ... (and reflections of refractions ...) low settings might introduce artefacts. And as demonstrated in various posts, one can have scenes with lots of mutual reflections, or complex shaped object with lots of self-reflections, or stacks of glasseous objects with lots of mutual refractions.

So in those cases, it's completely up to you to balance render time with artefact reduction as some reflection-intensive areas may be at the backside of objects not visible in the final result at all.

As the mutual ... thing is demonstrated so ofted for reflections, here are some refraction samples. No transparency, no IDL, just refraction.

And again, the Bounces value in Render Settings addresses both IDL and raytracing ans maxes to 12 even in the value box, so one has to use the D3D script instead for anything different.

Edit: in the meantime, be aware of the double-bend error in raytraced refraction. Refraction should bend a ray to the left then to the right or vice versa, but is Poser it bends the same direction twice which is wrong.

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Usually I'm wrong. But to be effective and efficient, I don't need to be correct or accurate.

visit www.aRtBeeWeb.nl (works) or Missing Manuals (tutorials & reviews) - both need an update though