v2 clouds indeed have their place. The new v3 model was implemented primarily to deal with more dense cloud volumes where internal multiple scattering effects have a much higher impact on perceived realism (think large cumulus, for example). The kind of low density mist you're talking about is really not a large challenge for most volumetric scattering models these days, including cloud v2, and since the simpler v2 model is faster, it of course makes sense to use v2 in that scenario. I think in most actual cloud situations v3 is going to give more realistic results - often notably more realistic - but the render time trade-off may not be worth it for everyone or in every situation.
All that is why v2 is still available in the UI. We have always had a focus on maintaining backward compatibility. You can still load and render most TG2 files without issue in TG4. But we have removed a number of older settings or shader versions because they were replaced by newer versions. That's not the case (yet, at least) with v3 clouds vs. v2. Both are still useful and thus both are available in the UI. We may indeed need to work on better naming to differentiate them more clearly and make their respective value more apparent.
- Oshyan
