If your image is exported without rendering shouldn't be any loos from the original. When the film i s rendered is re-compressed. This doesn't meen a loos, because if you had made a color correction your film will look better. But imagin that you just crop a little your image. Your image is rendered and recompressed. It don't gonna look better than the orginal.
I made few test with DV files (in FC) to see the loos in quality with few generations. I couldn't apreciate any loos in the first gerations, but after de second generation, the degradation of the picture was noticeable. In PP I don't know, but in FC, when you export you can choose "Recompress film' or not. If you choose yes, all the image is recompressed. If not, only the images that you have transformed or applied filters are re-compressed.
Normaly I film and edit MiniDV, but when I export I use a better codec tu keep what you have done in post-production. If you go export as DV, you waist a lot of what you have got. Only back to DV to "print to video". When I master a DVD I export with 10b Uncompress or so to keep all the color correction results and god graphics.