A one-word accusative circumstance is usually recognizable through its grammatical marking and relation to the host construction. A whole clausal circumstance, however, ordinarily needs a link (rābiṭ) to the bearer of the ḥāl. Otherwise the listener may hear an unrelated independent assertion.
The link shows that the later clause describes the state of the participant already involved in the main event. Its choice therefore protects the intended semantic attachment, not merely the surface rhythm of the utterance.