I use it in Weather to switch between forecast displays. And occasionally to customize watch faces. But I don't like doing it, because it leaves beautiful smudges all over my otherwise clean display.
Use it all the time to clear multiple incoming notifications messages that mount up. So, instead of clearing them one at a time (swipe, x, swipe, x, swipe, x...) Just one force touch, clear all.
Mine stopped working but I used it all the time to clear notifications. Now it doesn't work. I'm going to open a ticket with support when I get paid. I want to do it before my AppleCare runs out.