Repetition may reinforce a report by repeating the sentence or a salient part of it. For example, “جَاءَ زَيْدٌ، جَاءَ زَيْدٌ” can strengthen the announcement of Zayd's arrival when repetition serves a real communicative purpose.
A supplementary particle (ḥarf zāʾid) is not a meaningless particle. In Arabic grammar an element described as supplementary may still reinforce meaning or provide another rhetorical benefit.
For example, “مَا جَاءَنِي مِنْ أَحَدٍ” uses an additional min to strengthen the universal scope of negation. Such analysis depends on specific grammatical conditions; a supplementary particle is not simply useless wording.