Elastic App Search provides a scalable solution for creating personalized search experiences across applications and websites by leveraging user search history. By tagging each analytics event with a unique user ID, developers can build a search client and an external controller that tracks user search terms and clicked documents to generate personalized search results. This involves querying the App Search analytics API for a user's top queries over a specified time range and using these to suggest relevant documents, potentially excluding previously clicked items for novelty. The system is flexible, allowing segmentation by various criteria such as geographic region, and can incorporate additional user data for more tailored results. Developers are advised to handle the analytics API with care to maintain security and can experiment with the feature using a free trial of App Search on Elastic Cloud.