I didn't actually explain it that well. Was really late here, so I didn't have my thinking hat on.
Better explanation: they aren't actually folders, they are still scenes. All you are doing when you type - at the beginning is telling the editor that the scene is a placeholder, which adds the folder icon to it & the option to collapse/uncollapse any scenes listed below it or between that placeholder & the next one below it.
Now, the placeholders are still technically scenes, which means you can still add images, scene objects, values, conditions, etc. In other words you can use them exactly the same as you would use scenes. They still get exported when you build/export your game.