Archive_command

I have a question related to the archive_command option of postgresql.conf.

In the documentation[1] I found examples that add a "< /dev/null" at the
end of the cp command. I know what the redirection from /dev/null does
(send an EOF), but is it really needed? In [2] there are examples that
don't have the redirection of STDIN from /dev/null.

[1]:
http://www.postgresql.org/docs/8.3/interactive/continuous-archiving.html
[2]:
http://www.postgresql.org/docs/8.3/interactive/runtime-config-wal.html#GUC-ARCHIVE-COMMAND