A great way to experiment with different versions of adjustments and develop work. A snapshot is a record of how an image looks at a certain point of development and you can get back to it with only one click. It’s helpful for saving your progress when you have complex development and they really come in handy when you want experiment without having to make multiple copies of your photo.
A virtual copy is not an actual copy of an image but it’s a new set of instructions for it, so it doesn’t take up a ton of disk space like an actual copy would. However virtual copies act like independent images and you can even add them to collections. They’re also very helpful when you want to try out different effects and perhaps make both black and white and color versions or take a different path.