Think of your app as a container with a core. The container contains all your plugins, splashscreen, anything native. The core is your actual html/js/css. When you build your app, the container and the core are packaged together and you can publish this on the App Store. The Ionic Pro Deploy allows you to post new “cores” in the Ionic git repository. When a user starts your app, it will check for a newer version of the core. If one is available, it will download it, replace it’s current core and run the newest version. This is great for quick updates to your code.
So in short, you need to publish at least once to the app store and then you can do quick updates using the Ionic Pro Deploy. The downside is that if you add plugins or change your splashscreen, those won’t get published with new cores. You need to package and publish a new version to the app store but since those additions are rare, you can take care of most of your small updates with Ionic’s Deploy method.