Gatsby's Valhalla Content Hub offers a versatile and unified data layer that allows developers to query data from any CMS, API, or database without being tied to the Gatsby framework itself. This tool simplifies the process of data integration across projects by eliminating the need to write complex code for fetching data from different sources, which is particularly beneficial for agencies managing multiple clients and content management systems like Contentful, WordPress, and Shopify. Paul Scanlon highlights his experience using Valhalla in combination with the Remix framework to build a project called NYC Diary, emphasizing the ease of use and efficiency gained by not having to delve deeply into various API documentations and instead using Apollo Studio for constructing queries. The hub is in early access and requires a Gatsby Cloud account, but it promises to streamline development workflows by reducing the time spent on data sourcing, thereby allowing developers to focus more on creative aspects of web development.