Halliday & Matthiessen (2014: 430-2):
Semantically, the effect of combining clauses into clause complexes is one of tighter integration in meaning: the sequences that are realised grammatically in a clause complex are construed as being sub-sequences within the total sequence of events that make up a whole episode in a narrative. … But the integrating and choreographing effect achieved by clause complexes is not, of course, restricted to narratives; it is a feature of texts of all kinds.