I pre-ordered the Apple Watch, given what I know what it can do now and assuming I never bought one, would I buy it again? No. Since I have bought one, I will keep buying them, and I know this sounds cliché, but it changes the way you use your phone.
Break it down into 3 tasks and the 4 platforms. Small, Medium, and Large tasks; Watch, iPhone, iPad, Mac.
Small tasks, -> scanning through emails, checking messages, checking notifications, making phone calls, favoriting songs, etc...
Medium tasks -> replying to emails, serious phone calls, browsing the web, lengthy message responses.
Large tasks -> editing photos and movies, writing documents, etc...
How it used to be:
phone - > small and medium tasks
iPad -> small, medium, and large tasks
Mac -> large tasks
How it is now:
watch -> small tasks
phone -> medium tasks
iPad -> medium and large tasks
Mac -> large tasks
Just having the small tasks on my watch makes a huge difference in how I use my phone, I can choose to reply to a message or wait in case it needs a longer response. Quick phone calls are easy.
It was easy before the watch, but the watch provides the ability to screen calls without pulling out your phone, check text messages without feeling like you have to reply right then.
Choice is up to the person really, but in my mind, I'm locked in with the Apple Watch.