I have yet to find anything about this so I'm posting what I found accidentally tonight.
If you use an SD card from the start of your saved data then it will save to the card for all your info, this is important. Simply insert the card into a computer and copy the "Nintendo" folder. Now you have a backup that can be copied to the same card if it loses its info or gets formatted. You can also upgrade your SD card to a higher capacity by first inserting the new card into the Switch and letting it prep for use on the console. Take that card and copy the saved "Nintendo" folder and its contents with the computer. It will recognize the saved files, pics/vids, and the higher capacity with no issues at all. I just verified it working properly several times and the game saves in the games themselves. Still can't share saved files yet that I'm aware of but you can now transfer data from one console to another, it just deletes it from the first console. Maybe Having two cards will allow for sharing...I will test soon.
If you use an SD card from the start of your saved data then it will save to the card for all your info, this is important. Simply insert the card into a computer and copy the "Nintendo" folder. Now you have a backup that can be copied to the same card if it loses its info or gets formatted. You can also upgrade your SD card to a higher capacity by first inserting the new card into the Switch and letting it prep for use on the console. Take that card and copy the saved "Nintendo" folder and its contents with the computer. It will recognize the saved files, pics/vids, and the higher capacity with no issues at all. I just verified it working properly several times and the game saves in the games themselves. Still can't share saved files yet that I'm aware of but you can now transfer data from one console to another, it just deletes it from the first console. Maybe Having two cards will allow for sharing...I will test soon.