ScandiPWA is a headless application and it requires a compatibility extension with conventional Magento 2 extensions to serve them for PWA applications. Specifically, it provides a GraphQL and React component to let the client-side render the application to be able to interact with the back-end of the extension. ScandiPWA rewrites Magento front-end, so it needs to replace the front-end layer of a usual Magento 2 extensions and this extension is providing exactly this.