This option is a real time saver as it will populate the current translation to all repeated segments in your working document after the changes are saved, so whenever you save translated segment(s) the system instantly translates all identical source texts anywhere else in the document. By default, propagation does not replace existing translations but only propagates to untranslated segments; however, you can change that to populate the translation to translated segments as well. If you are afraid of any faulty translation, then you can disable the auto propagation option and choose to propagate “on-demand” from a segment’s context menu, instead.