I could occasionally get hitched up by small frame delays in timing-reliant games like Celeste, but it was unnoticeably smooth more often than not. Then you can play PC games from your Android device, assuming the network connection is fast enough. It's possible that black bars on the edges will appear on your mobile device since this is how the app is dealing with the aspect ratio differences, but you can use two-finger pinch and pan gestures to zoom in.
The potential for bathroom gaming is limitless. With it, you can play your collection of Steam titles on your smartphone, provided you've a powerful computer to run said games and you're under the same roof. The Steam Link app also works with Android TV set-top boxes, providing it's connected to the same router as your PC.
Is my existing Steam Link hardware still useful? This means that gamers with Android devices will be able to take it for a spin, but note that since the app is in beta, it means that there might be some kinks that have yet to be worked out, and features that aren't necessarily guaranteed to make the final cut.
That said, even the Apple TV version has a major drawback: controller options.
I also wonder if game developers can bake in touch support for strategy games and RPGs so they're easier to play without a controller - it'd be a blast to command armies of Incas to slay the invading Conquistadors while lying in bed.
The Steam Link app supports Android 5.0 and the Steam Controller or other Bluetooth input devices. Beyond using the clunky touch controls.