Āthār al-ṣaḥābah are transmitted statements, judgments and practices of the Companions. When two Prophetic reports seem to point in different directions, Companion practice may show how the generation closest to the Prophet understood their use.
One report may appear general while another supplies a limitation. A well-established Companion practice can assist in deciding which application is appropriate.
This does not elevate a Companion report above the Quran. Its relevant function is as supporting evidence for interpreting and weighing the competing Sunnah reports.