Turning a User-Interface Extension (UIE) into an app doesn't require many code changes, but it gives access to new powerful features built on the same underlying technologies that run UI extensions. This transition allows for more custom functionality and integration with Contentful and third-party products to meet business needs. Apps are portable solutions for developers working with Contentful regularly, providing a repeatable way to shore up custom functionality without needing extensive code changes. The migration benefits include customizable configuration, personal webhooks, the ability to act as a user and listen for data changes, sharing across environments, and keeping UIEs up-to-date. Developers can migrate by creating an AppDefinition blueprint and hosting their UIE on the internet, with optional advanced features like custom configuration screens.