3D Touch (before called Force Touch) has been in Apple products since 2014. I use it all the time on iPhone 7S, it's a regular part of interacting with the operating system:

- force touch an image to view fullscreen

- force touch app icons to open a quick menu

- force touch buttons in Control Center to open a menu

It's like a quicker touch-and-hold action in other operating systems, although sometimes there's also a touch-and-hold action in iOS which can be annoying.

Yes, I use it all the time. Mainly app-switching and text navigation (3d-touch/force-press on keyboard to enable floating cursor mode).

It initially came off as a gimmicky way of 'right clicking' but has evolved into more than that. Software has also been refined since first release.

Having used an iPhone with pressure sensitive screen the past year, it remains unused for me, partly because the gesture feels unnatural and partly since most apps don't support it, I dont expect it to do anything.