-dit(bf(--blocking-io)) This specifies whether rsync will use blocking
-IO when launching a remote shell transport. You may find this is
-needed for some remote shells that can't handle the default
-non-blocking IO.
+dit(bf(--blocking-io)) This tells rsync to use blocking IO when launching
+a remote shell transport. If -e or --rsh are not specified or are set to
+the default "rsh", this defaults to blocking IO, otherwise it defaults to
+non-blocking IO. You may find the --blocking-io option is needed for some
+remote shells that can't handle non-blocking IO. Ssh prefers blocking IO.