Quote - Yeah, basic rule #1 - never use "volumetric world".  ;o)

HDRI - pretty much moot if you have an indoor scene with walls and ceilings, imo. That kind of scene wouldn't benefit from hdri. I mean you already have a full enviroment for reflections, trnsparencies and refractions. And, in real life, in an indoor room, there would be lamps/candles and such somewhere, just place spots and radials there.

Not having Bryce in my toolbox of applications, I can't say for sure, but you may be able to utilize HDRI to simulate "bounced" light in an enclosed room.  Or perhaps Bryce already has light bouncing or another way to fake GI for such things.  Note that simple GI is different that HDRI in that GI can be used as a way to bounce photons around a 3D room from existing lights in a scene..

For example, you could theoretically make your own simple, custom HDRI to "compliment" the indoor lighting setup you have in an indoor scene, and use it to simulate secondary light bounces from your light sources, and give the scene some soft ambient (AO-style) shadows..  That is, if Bryce doesn't already have another way of doing this that's more accurate/direct.

A better example of this would be to place one radial light in a room.  Normally, the light will end where the falloff ends, and the rest of the room will be black.  Plus, you won't get soft ambient shadows where you would expect them, because there's no light bouncing around in there from your single light source.  A low-intensity, solid-grey lightprobe could be used as "fill" lighting to provide the faked light bounces, instead of adding a multitude of standard lights.  Of course, it will only work if you can use HDRI in an enclosed scene in the first place.  If Bryce impliments HDRI like a skylight, then you'd have to take the roof off your room in order for the probelight to get in there.  This would actually be the kind of situation where IBL/AO or standard GI (photon mapping) would come in very handy.

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