If you want to unlock your Mac with your Apple Watch this work terrifically. My one caveat is that it is a tad slower than when I use the Touch ID sensor on my 2016 MacBook Pro, but it is still a nice feature to have activated either way. If you don't have the new MacBook Pro with the Touch ID sensor then it is a no-brainer to activate. Not only is your Apple ID better secured with 2-factor authentication; but, you are also able to access your Mac easier without the hassle of needing to type in your password each time.
I one thing I should mention, this does not work when you power your Mac on, you will still need to enter your password in that situation. If you are waking your Mac from sleeping though, it works every single time.
Once you set-up your Apple Watch to unlock your Mac, when the Watch is used to unlock your Mac you will get a tap on the wrist and hear a jingle on the Watch letting you know it just unlocked your Mac. You will also see a notification on your Watch as well. I have noticed that it doesn't unlock my Mac unless I am sitting right in front of it, which is a good thing for security reasons. I do not want it unlocking my MacBook when I am not at my desk but I am in the same room as my MacBook. It works perfectly!
You do need to have a mid-2013 Mac, running macOS Sierra 10.12 or later, and your Apple Watch needs to be updated to watchOS 3.
Below you will find a few links to the Apple Support sections for each aspect of using your Apple Watch to unlock your Mac.
2-factor Authentication information:
Unlock your Mac with your Apple Watch information: