Spoiler: They don't do much. It's full screen or bust.

The Galaxy S8 has an intriguing, and tall, screen with a unique 18.5:9 aspect ratio. While most Android apps are able to easily scale up to fill that extra screen height, some are hard-coded to stay at 16:9, leaving black bars between the notification shade and the on-screen navigation keys. These are not only awkward and distracting, but they also don't have to be there!

Is there any downside to enabling fullscreen mode?

If there is, we haven't found any. Some games may not look exactly as they were meant to when forced to run in fullscreen mode, but we haven't found that to be the case with any that we play regularly.

How to enable full screen apps on the Galaxy S8

  1. Hop into Settings.
  2. Tap on Display.
  3. Tap on Full screen apps.
  4. Enable the apps that aren't highlighted by default.

From here, you can choose which apps you want to utilize the full-screen aspect ratio.

You'll know when full-screen scaling is off if there are black bars on the top and bottom of the app next time you launch it.