I guess it depends on if you have (and are used to having) you phone make a noise when you receive notifications. I have most notifications set to silent, and some I let vibrate. The only thing that makes a sound is my alarm and calls.

Since smart phones became a thing I've always had them set to vibrate, I don't really see why you need your phone to make a sound (and disturb other people) when you get such things as an Instagram like or a game wanting you to play more. Biggest quality of life improvement was disabling vibrate (so it's silent) for instant messages and SMS (which my phone always notifies me twice about?) - they can wait a few minutes to hours and don't need instant replies.

They tested power-off vs power-on. No results on face-up vs face-down, but they probably didn't record it.