There is one case where I could see that it might make sense to burn SD material to BD: home video.
If I have an hour-long video taken with my miniDV camcorder, it will take up 12-13 GB on disc when I import it. That video then gets compressed to fit on a 4.7 GB DVD. With Blu-ray, I would assume it could be burned to disc without any further compression, resulting in a better image than a DVD would provide.
In theory, this ought to work. Does anyone know if it's practical to actually do?