-they are not empty. This applies to both the --delete option and to
-cases where rsync tries to copy a normal file but the destination
-contains a directory of the same name.
-
-Since this option was added, deletions were reordered to be done depth-first
-so it is hardly ever needed anymore except in very obscure cases.
+they are not empty when they are to be replaced by non-directories. This
+is only relevant without --delete because deletions are now done depth-first.
+Requires the --recursive option (which is implied by -a) to have any effect.