As you know, High Sierra (HS) includes a feature called “file cloning.” [EDITORIAL NOTE: Initially I'd written that, based on my discussion with the developer, I gathered Carbon Copy Cloner (CCC) can't back up cloned files. He's since clarified that CCC can't save cloned files as cloned files — it still does save files that have been cloned, but as complete files, rather than binary deltas. So all your files are properly backed up with CCC; it's just that the backup may take up more space than the original.]
1) What actions do vs. don't create cloned files in HS? I did some of my own testing, and here's what I found:
I went to Finder-> Macintosh HD (in the sidebar, under Devices)-> Get Info. I then monitored the spaced used.
A) Duplicated two 3 GB data files in Finder (cmd-C then cmd-V). Here the space used didn't increase, indicating this procedure probably does create clones.
B) Opened a 128 MB data file in Excel. I then created a duplicate from within the program, using File->Save As. Here, the disk usage did increase correspondingly. [I did try using a larger data file, but it was taking too long.]
C) Opened a 500 MB data file in TextEdit. I then created a duplicate from within the program, using File->Duplicate. Here, the disk usage did increase correspondingly. [I did try using a larger data file, but it was taking too long.]
Preliminary conclusion: Creating a duplicate within Finder results in a binary delta. Creating a duplicate within applications, both Apple and non-Apple, results in a separate stand-alone file (and takes much longer than creating a duplicate in Finder).
2) In addition to using CCC, I create parallel backups using Time Machine (though I prefer the former). I’m curious if the cloning function is also used to make Time Machine more efficient for non-cloned files. What I mean is this: In older OS’s, if a file had changed, Time Machine had to save the entire updated file. Thus, if one was using Entourage, where all emails were stored as a single multi-GB file, one would quickly fill up a Time Machine partition, since Time Machine would have to store a new multi-GB file with each backup. What I’m wondering is if, with High Sierra, Time Machine now only stores deltas of each backed-up file (i.e., just what’s changed). [EDIT: It appears this part has been answered in the discussion section, below: APFS doesn't change Time Machine's behavior, which was always to create binary deltas when the file configuration allowed it.]