Halliday & Matthiessen (2014: 434-5):
These grammatical opportunities for realising a sequence of projection or expansion form a scale defined by two poles: one pole is the simple clause with a circumstantial element and the other is the cohesive sequence of two independent clauses. The clause complex thus covers the region intermediate between these two poles. … closer to the pole of circumstantial augmentation, there are clause combinations where one clause is dependent on a dominant clause, the two thus being of unequal status [hypotaxis]; closer to the pole of cohesive sequences, there are clause combinations where the two clauses are interdependent on one another, the two having equal status [parataxis]. This scale of degree of grammatical integration and interdependence in the realisation of projection and expansion is represented diagrammatically in Figure 7-2.