Q2: (not 100%) this probably wouldn't apply if crossing fs boundaries, and so cloning to another filesystem would probably occupy more space than the source one

Q2: (not 100%) this probably wouldn't apply if crossing fs boundaries, and so cloning to another filesystem would probably occupy more space than the source one. Also, many save out files to temporary copies, remove the old file, and move the new one into place. That likely wouldn't track either. Not really 'immediate safety' of the file, but secondary concerns.. Similar caveats apply for traditional soft/hardlinks and sparse files.