Two weeks ago, I updated my Macbook to High Sierra, and I updated my Apple Watch to Watch OS 3. I can’t tell you about any notable changes to either software, but I can tell you about one feature that has made my Apple Watch indispensable to my daily routine.
Auto Unlock. If you’re wearing your Apple Watch, your Watch will auto-unlock your Macbook in milliseconds, and you no longer need to type in your computer’s login password. I estimate that this single feature will save me ~10 hours per year. More importantly, my concentration is no longer interrupted by the need to enter to my password each time I want to start typing.
There are some other reasons to get the Apple Watch, but this is a reason the watch has become indispensable.
Details on how to set this up: https://www.imore.com/auto-unlock