Halliday & Matthiessen (1999: 205):
As with names of projections, names of expansions often serve a rôle in creating cohesion in discourse: e.g Instances such as these … , Another way of approaching the situation … , That aspect hadn’t occurred to me. Such expressions construe preceding figures and sequences as participants in their turn, and so enable the speaker or writer to make explicit the organisation of the discourse itself.