Data Used Is Larger in APFS Volume Than in Cloned Mac OS Extended (Journaled) Volumes

I have a 27" Retina 5K iMac with a 1 TB SSD (OEM) running High Sierra 10.13.4. The amount of APFS used space is 342.69 GB on disk. I have used the latest version of Carbon Copy Cloner (5.1.2) to clone to two external spinning platter drives formatted Mac OS Extended (Journaled). One drive shows 259.41 GB of used space and the other shows 260.27 GB of used space. Both external drives were cloned one after the other in the same hour.

Why is the AFPS figure roughly 80 GB larger for the same data? Is it the APFS snapshots, which I don't understand?