Halliday & Matthiessen (2014: 461-2):
In terms of realisation, the two tactic forms of elaboration have one property in common — tone concord. That is, each clause in an elaborating clause nexus is realised by a tone group, and each tone group selects the same tone … . However, hypotactic elaborating clauses differ from paratactic ones in that they have their own grammar — the grammar of relative clauses … . In terms of meaning, paratactic elaboration and hypotactic elaboration are largely complementary, covering different aspects of elaboration. Paratactic elaboration involves exposition, exemplification and clarification, while hypotactic elaboration involves description.