I can assure you that the number of plygons isn't the most time consuming thing when it comes to rendering. Rendering 50 000 polys or 200 000 isn't that much of a time difference.


Sometimes (very often) you want the best possible quality of the render and then you don't care how long it takes. And it's up to you of you want quality or speed. And an unbiased renderer is far more easy to set up and gives more realistic results than "normal" render engines. However they take far more longer time.