The folder wp-content/sn-backups/ is created and used by the plugin when you use one of the auto-fixes.
The plugin takes a quick backup of any file that needs to be modified and saves a backup just in case the fix breaks something and the site can be restored much quicker by having a backup.
The files are saved just in case an issue occurs, but other than that the files can be deleted once you have tested the website still works properly.
