Halliday & Matthiessen (2014: 654):
Unlike REFERENCE and ELLIPSIS, the resource of LEXICAL COHESION is, in general, neutral with respect to textual statuses; that is why we have not included it in Table 9-4. A given lexical item can be assigned any of the textual statuses; it is not predisposed to any particular status. Similarly, a given lexical relation is also neutral with respect to textual statuses. However, a particular lexical chain in a text is very likely to show some systematic pattern in relation to textual status.