Cloning makes and exact copy of one disk to another disk so if your disk dies you plug in the other disk and its done. An image is also an exact copy but saved in a compressed file and needs to be restored to the disk. The advantage to the image is you can save multiple copies and select which one you want to restore. So if you have a problem with you disk and it can be re-formatted and is OK then the image can be restored to that same disk. If your disk does go bad you can use the image to restore to a new disk. Macrium also has a feature that the image can be mounted and individual files can be restored.

Jim