4:3 makes better use of the image circle from the lens than 3:2, about 4% more of the same image circle used.
4R is set at 6" x 4" which is 3:2. 8R is 10" x 8" which is 5:4.
On video, the preferred ratio is 16:9, which is more to our eye's width. HDTV is 16:9. Standard TV ratio is 4:3, and it is also the standard monitor ratio.