I guess the main reason to have an emuNAND is to be able to update it while keeping the lower firmware on the regular NAND for easier access to Atmosphere. I don't know if a coldboot is possible in 5.0.2, but if it were, it might be made more difficult to achieve in later firmwares. So keeping your regular NAND on a lower firmware does have its advantages.
Of course, the lower your firmware in the first place, the better.
SysNAND should always be up to date if you still want to be able to update your games or use the nintendont online services which most probably do not want to do without.











