The 'Schema App Structured Data' plugin plays an integral role in the search engine optimization of any WordPress website. But how does it do this? The answer lies in understanding "structured data". Structured data is a type of code that makes it easier for search engines to crawl, organize, and display your content. By using detailed tags or labels, structured data enhances the utility of your site’s information, making it more digestible for engines like Google.

The 'Schema App Structured Data' plugin primarily assists in this process by automatically structuring your website data to be easily understood by search engines. It integrates with your WordPress site and uses advanced JSON-LD (JavaScript Object Notation for Linked Data) format to mark up your website content with appropriate schema.org categories and attributes. This allows search engines to effectively contextualize your website content and thereby, presenting it in the best light possible.

Moreover, this plugin streamlines the structured data process, eliminating the need for manual editing of code. It automatically updates your site's markup when you publish new posts or pages, ensuring your site is consistently optimized. It can be used in conjunction with a multitude of other project types like WooCommerce and Easy Digital Downloads, thus providing wide applicability.

Part of its charm is the ease of customization it provides. For instance, if your website publishes reviews, the plugin enables you to markup review data according to schema.org standards, aiding search engines in comprehending that your content is review-based.

Moreover, this plugin also assists in the creation of "rich snippets". Rich snippets are the search results that have extra information or 'snippets' - these could be star ratings, images, or prices. Rich snippets have been shown to significantly improve click-through rates and drive more traffic to your site, enhancing overall SEO performance.