Ad Customizers allow advertisers to dynamically populate ad text with real-time data from a feed. This provides flexibility to insert different text, numbers, or values into ads based on factors like location, device, or search terms. The document outlines how to set up an Ad Customizer feed to store product and pricing data, then populate ads with placeholders that retrieve values from the feed in real-time. Limitations include character limits and needing a standard text ad as a fallback if no feed value is specified.