Imagine this example: You have a 32GB SD card. You are using 1.8GB of space on it. You want to back it up into an image that is 1.8GB big, not 32GB big. Then you want to be able to put it on an SD card that is 2,4,8 or 16GB big. If you do a normal image backup, you'll end up with an image that is 3...