Understanding Intelligent Sector Copy
When backing up a disk or partition you can select to do so using Intelligent Sector Copy. This is the recommended method for creating images. Using this method will result in smaller images and create them with greater speed.
How does it work ? In the case of a full image, Macrium Reflect will take a snapshot and then save only the clusters that are in use on the disk. In the case of a differential or an incremental, after the snapshot has been taken, Macrium Reflect will compare the clusters in use with the previous image and then save only those clusters that have been modified.