Halliday & Matthiessen (2004: 439-40):
When clauses are combined with the status of equal, there is a closely agnate version where the two clauses are not brought together structurally in a clause complex but rather form a cohesive sequence:
Kukul crouched low to the ground. He moved slowly.
In this version the elliptical Subject of the second clause has to be reinstated, since such Subject ellipsis is not possible outside the domain of a clause complex.
The two versions are treated differently in the graphology: in the cohesive sequence, the two clauses are separated by a full stop; but in the clause complex, there is no full stop separating the clauses (though there could have been a comma or even semi-colon).
This reflects the typical realisation in the phonology: in the cohesive sequence, the first clause would be spoken on tone 1 (falling), and then followed by the second clause also on tone 1; but in the clause complex, the first clause would be spoken on tone 3 (level), and then followed by the second clause on tone 1. Here tone 3 indicates that there is more to come – by the expansion of the clause to form a clause complex.