Can I use wp_editor() to create a second instance of the editor in my post page?

You can always use wp_editor on the admin end. One such situation may be by using metabox. In this case let’s say you want to manage custom description about the post. So instead of a simple textarea, you can use wp_editor.

Ex:

In the example given in the above add_meta_box Codex url, you can replace

echo '<input type="text" id="myplugin_new_field" name="myplugin_new_field" value="' . esc_attr( $value ) . '" size="25" />';

by

echo wp_editor( esc_attr( $value ), 'myplugin_new_field' );

You can try out the above code by adding into active theme’s functions.php file. Once you do this, you should see an editor now.