If you're somewhere with poor (or no) network connectivity you can still use Google Files or AirDrop (I believe, not 100% sure on AirDrop).
The pilot had taken a video of the Falcon 9 second stage separating from the first on its first launch that docked with the ISS. He then walked through the cabin sharing with anyone that was interested.
The point is, options are good. Most of us subscribe to the Unix philosophy of "Write programs that do one thing and do it well" so why are so many advocating for a pancea solution that does everything for every use case?
If I remember correctly, you can configure (I don't know what the default is) to power save or even turn off WiFi on Android when you turn off the screen. Are you sure that's not interfering with this beta app?