From the manpage of rsync-b, --backupWith this option, preexisting destination files are renamed as each  file is transferred or deleted. You can control where the backup file  goes and what (if any) suffix gets appended using the --backup- dir  and --suffix options.Note that if you don't specify --backup-dir, (1) the --omit-dir-times  option will be implied.What is the reason that if you don't specify --backup-dir, (1) the --omit-dir-times option will be implied?Thanks.
Why if you don't specify --backup-dir, the --omit-dir-times option will be implied?
rsync