Facebook Custom Audiences offers a targeted approach to marketing businesses by curating groups of people with relationships to the business or those who may be interested, and then engaging them through automated campaigns using Zapier's automation capabilities. The feature allows for four types of Custom Audiences: customer lists, website visitors, engagement, and app activity. Using automation can help build more effective targeted marketing campaigns by syncing data from various sources such as email platforms, websites, social media, and CRM systems, ensuring that ads reach the most likely customers.