You might find yourself in a situation that requires you to hand over access to your account under stressful conditions. Ghost Folders allow you to hide certain files, giving you deniability in these situations.
When you make a Ghost (hidden) Folder, this folder is temporarily removed from your account. It can only be brought back (summoned) by typing its exact name in the "Summon Ghost Folder" field. This way, you can deny the existence of the folder entirely.