Automatically Free Up Space on Your iPhone
If you chose the 64GB iPhone 8 or iPhone 8 Plus you can turn on one setting and it will automatically free up storage for you over time so that it's harder to run out of space on your iPhone.
The iPhone can uninstall unused apps so they don't take up space you need for photos, apps and installing updates. With this setting on, an unused app will be automatically removed, but you will still have the app data on your iPhone so it's easy to get going again if you need to. If you are bad about uninstalling apps you no longer use, this is for you.
Go to Settings -> iTunes & App Store -> Offload Unused Apps -> On.