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.