Tags allow you to group items inside a specific collection. Then, you can create on-device bundles including one of those subsets. (You can download several on-device bundles to a device, but you can only use one tag for each bundle.)
You can assign tags to specific items based on the logic that your app requires. For example, you can differentiate between categories, or group items allocated to the different users - so that only the items that belong to the specific user will be embedded in the app on the user’s device.
This way, you can make sure that your on-device apps weigh only as much as needed, as the users only get to download relevant personalized content.