This features works in one of two modes: Push or Pull. In Push mode, Media Cloud will upload your assets to cloud storage. In Pull mode, your asset URLs will be rewritten to use a CDN host that will fetch those assets from your server automatically.
For best performance we recommend Pull mode. Push mode requires Media Cloud to upload these assets and it will only upload them the first time they are used in your front-end. This upload will only happen once, of course, so subsequent requests will be fast as they will come directly from cloud storage.