Why to write applet config for dbus?

There is a tutorial http://wiki.mate-desktop.org/matecorba_to_dbus#d-bus_service_file which says how to create DBus configuration file. But I don't understood, why it is required. The service is registered by applet itself during the applet's startup. And applet's startup is described in another config (in config of mate-panel). So, when DBus starts the applet independently from mate-panel?