Its first purpose is eligibility for rich results — review stars, prices, event dates, breadcrumbs — which change how a listing looks and how often it is clicked without changing its position. Its second, increasingly important purpose is disambiguation: telling machines exactly what entity a page describes, which matters as much to answer engines as to search results.
Accuracy is not optional. Markup that describes something the page does not show breaches Google's structured data guidelines and can trigger a manual action; the Rich Results Test and the Search Console enhancement reports are the check. Mark up what is genuinely on the page, keep it in sync when the template changes, and do not invent ratings.