Cloning is for changing the drive
right now.
Imaging is for backups, to be potentially used in the future.
The Rescue boot CD or USB is for when your OS drive dies, and you need to recover to a new drive from one of the Images you created.
My system has 7 physical drives. A direct clone of each would require another 7 physical drives.
Images, and I can store 30 days of Full/Incremental images for all 7 drives, on a single target drive (actually a folder in my NAS box).
Cloning is a snapshot of right now.
Images, I can go back in time. If something weird happens and I don't notice for a couple of days. I need the image from the day
before the BadThing happened. No problem.
Here are the folders for the drives in my main system. Each drive gets its own folder.
Inside each is up to 30 individual Images, either Full or Incremental.
Imaging runs at night, between midnight and 4AM.
There is similar for all the other systems in the house.
That is in my NAS box, but could just as easily be on a large external USB drive.