I got tipped over the edge two weeks ago when I watched the Apple iOS announcements at WWDC, and bought an Apple Watch. I have been thinking about it for the last year or so, but never found the killer app. The announcements of the improvements to Siri in iOS 12 convinced me.
Other than for future Siri, I finally caved and bought one basically for two reasons: 1) it was something I could wear all the time and call for help if I needed it (I am in my mid-70s and live alone), and 2) as a health monitor.
In regards the the health monitoring functions, I read the Apple User Guide section on the Activity function twice and still didn’t quite understand some of the details of how that feature worked. It took about a week and a half to finally get it figured out. I am still a bit puzzled by the fact that I can do a casual Outdoor or Indoor Walking Workout, and it does not count as Exercise (but shows up as a workout). I surmise that the difference is triggered by the heart rate monitor at some point: too low a heart rate and it's not a workout (sounds reasonable when I think about it). I use both a stationary bicycle and a treadmill for my indoor exercises.
I have already seen some benefit in having it remind me of daily goals… It seems to be helping me get around a bit better with my dodgy knees after only a week and a half.
The screen is a bit small for reading books, however.