This is an old revision of the document!
A whole bunch of Xfce uses DBus communication (xfconf, thunar, xfce4-panel, xfce4-session, xfce4-appfinder, tumbler). Most of this is done through generating dbus binding (xml > dbus-binding-tool > code) and using the dbus-glib library.
Since 2.26 glib has its own implementation for this to replace dbus-glib, so it is wise to switch to this API and drop dbus-glib.
Advantages are: gdbus does not include the dbus library and uses GIO streams. It's therefore a lighter implementation. dbus-glib is also not maintained as much as gdbus.