A nominal circumstance may already contain a pronoun referring to the earlier bearer, yet an additional wāw can remain useful. The pronoun identifies whose circumstance is involved; wāw can clarify that the independent-looking predication is subordinate to the preceding action as an attendant state.
In جَاءَ زَيْدٌ وَأَبُوهُ مَرِيضٌ, the pronoun of abūhu connects the father to Zayd and wāw presents the following report as a circumstantial accompaniment. Removing wāw may still permit a reading, but increases the chance of a separate assertion.