Even amateur's can use the data to make better workout decisions that lead to better outcomes, too. My workouts and quality of life are objectively better by using a smartwatch, and I'm a bit surprised by the luddites here on hacker news of all places.
Oh well, the markets have clearly spoken about the objective benefits of smartwatches.
I'm sure it's my bubble, but all the runners I know run with watches at least. Almost all of them use some form of GPS watches. It's nice to be able to go outside and just run, and not worry about routes when you want to do anything more than a few miles.
Running with nothing is great except if you want to make data driven decisions to optimize your training. Even basic speed work requires a timer and a track. (Or just a smartwatch).
As a runner, I used to pop on a garmin gps device and go for runs to help measure my training. Some days I would measure my heart rate with a chest strap to help my training. Apple watch, while generally not as good, it is good enough, and is something I can just wear all the time and provides the same functionality.
It also has a lot of extra features like unlocking your computer without typing a password, allowing you to respond to text messages without getting out of the shower, etc. It really does provide a lot of value.
Allowing you to ping your phone is also incredible when your toddler likes to grab things and puts them in random places.