I often see post of images with render times and the number of samples for the finished scene. I have seen post where 1000 samples were used and some with as few as 50. I know that some sampling is determined by the complexity of the scene. The computer and hardware has a little to do with it as well.
Since I have no technical background in the coding for cycles nor could I give a definitive outline of the best hardware everything here is based on my own test and research.
If you are fortunate enough to have an up to date nvidia graphics card you will more than likely get the benefit off lightning fast renders with reduced noise. For those of us still rendering on cpu the challenge is finding a balance of quality and speed to get the most out of cycles.
The first test I did was the Mike Pan bmw bench mark. I used cpu rendering as I have an older nvidia card which is not supported. The computer he used is basically the same as mine and with 200 samples his time 8 minutes and 9 seconds for the scene set at 200 samples. My render time was 6 minutes and 50 seconds. If I used these setting to do a 10 second animation it would take 1 day plus 5 hours and 17 minutes. For about 180.00 dollars you could buy a gtx 570 and render the scene in 53 seconds or the 10 second animation in 4 hours.
So with all that said, who wants to spend hours working on a scene and the wait another half a day to see the finished result.now me personally I do not have the patience. I have tried to learn Blender and use cycles but for some of the things I would like to do, cycles just seems to take forever. After viewing this presentation a tried a few things not in any particular order and I came up with this.
This image was done using path tracing 200 samples and took 50 minutes and 52 seconds.
This image was done using the branch path tracing itegrator 20 aa samples 1 diffussed 5 transmission 1 ao, mesh light and subsurface. it took 2minutes and 52 seconds.
This image is basically the same as above but it only used 10 aa samples and it took 1 minute and 32 seconds.
This 30 second animation took 4 1/2 hours to render. The bottom line is spend the money and get a good graphics card.
Now it may just be me but there isn’t much difference in the image quality and all render times naturally included the compositing. I would like to get to where a scene takes 30 seconds or less to render which would be very practicle for animations