I have all sounds and vibrations turned off. Works great in conjunction with an Apple watch that has vibrations turned on. Not arguing with your percentage guess; I'd guess the same thing... just saying there are some of us :-).

Edit: BTW the described idea probably wouldn't work with my Apple watch setup, because it seems there can be some latency between the iPhone and the watch with respect to notifications. I wouldn't want to get a vibration on the watch then be wondering for a few seconds "when is something going to pop up on my phone?" I realize technically the notification comes to the phone first under the hood... but where it is displayed first is a matter of programming.