I looked up `-c` on macOS. It says it causes cp to use clonefile(2) instead of copyfile. So I looked up clonefile(2). It says: NAME clonefile – cr

I looked up `-c` on macOS. It says it causes cp to use clonefile(2) instead of copyfile. So I looked up clonefile(2). It says: NAME clonefile – create copy on write clones of files SYNOPSIS ... LIMITATIONS Cloning directories with these functions is strongly discouraged. Use copyfile(3) to clone directories instead. But no explanation of why strongly discouraged.