The Song Editor can be used to insert or remove parts of a song. It always works in 'Ripple mode', regardless of the Ripple button at the top of the main window. The song editor works in 'bar mode' if there are any MIDI tracks, regardless of the Bars button at the top of the main window.
The song editor affects "everything":
The Song Editor can't be used while the transport is running.
Song Editor window