As for being able to use your data on another 3DS in the event you lose it, it gets stolen, bricked etc.
As long as you have a NAND backup and GodMode9 essentials backup, that's all you need to decrypt your NAND on a PC and access its contents and potentially do a manual system transfer of all your games, friend list etc. to another 3DS (if you still have the SD card contents)
Only the NAND backup (and optionally SD card backup if you want a backup of all your games too) needs to be updated when you install new things. The essentials backup just contains some keys needed in order to decrypt the NAND so it doesn't change.