One note I will add to this based on a bit of discussion I have seen in VFX circles: if a scene involves a lot of big textures or anything of large size loaded off of disk or off the network, it could impact rendering performance. In most cases Terragen loads everything into memory before rendering, so if there were to be a hit I would guess it'd be in scene load time. But I think this is more likely to affect those renderers that try to be more clever with mipmapping, disk caching, etc. Terragen's simplicity is a strength in this case.
- Oshyan