Well, let me explain better, because Carrara takes time to calculate the lighting on the surfaces replicated and therefore renders even more slowly, then if has not to calculate an entire ecosystem will do all the task in a very quickly time; for example, I rendered a frame of my " river valley" with and without the eocsystem behind the camera, and the result:  7'22 against 10'20, and this happens in a clear manner with complex environments; I tried in Vue and the gain is not so clear, in some cases, the rendering time is longer because of the sky; I'm gonna test also with C4D; anyway with such saving time, to me you can define a cool "bug". ciao