Complete disjunction normally requires separation only when omission of wāw does not itself lead to an unintended interpretation. Two unrelated statements placed immediately together might otherwise be mistaken for an answer-and-explanation sequence.
This explains the separate categories of complete disjunction without ambiguity and with ambiguity. The first calls for faṣl; the second may call for waṣl to avoid the misleading implication. Their detailed examples belong to the subsequent discussion.