Chance Miller, in this 9to5Mac op-ed piece:

What I love most about Face ID is that it’s passive. It works without me needing to do anything, such as place my finger on a fingerprint reader. Need to view my Safari Keychain? Face ID authenticates me. Opening a secure app such as a banking app? Face ID to the rescue. On the Mac, Face ID would be able to do all of this in an even more seamless fashion.

For instance, unlocking your Mac would become an automatic process. By the time you sat down and opened your MacBook, Face ID could recognize and authenticate you – there’d be no waiting involved. Similar to how Auto Unlock works when your Mac is paired to your Apple Watch, logging in would be a completely passive and secure process.

I have mixed feelings about this. I use my Apple Watch to unlock my Mac and, once it’s unlocked, it tends to stay unlocked for long stretches. I unlock my Mac from 2-10 times a day, at most. My phone on the other hand, can require an unlock as many as 100 times a day.

My point is that I don’t think the cost of adding Face ID to a Mac, purely for unlock, would be worth the expense to me, given that I have an Apple Watch.

But:

In terms of broader security, Face ID would bring major improvements to the Mac. Currently, if you have passwords and log-in information stored in Safari, macOS doesn’t prompt you for any authentication when you go to sign-in to a website. Apple assumes that the initial log-in to macOS was enough authentication, and while this is true in most cases, it still represents a potential security hole if someone were to get ahold of your Mac after you’d already logged in.

The key would be if Apple tightly integrated Face ID throughout the operating system, as they did with Touch ID and Face ID throughout iOS. And, of course, I would expect Apple to do that.

But I think Face ID on the Mac would go way beyond security. For starters, the facial mapping would allow you to use Animoji throughout macOS. More importantly, whatever technology follows Animoji in taking advantage of facial mapping will also be possible on your Mac.

As augmented reality evolves, facial mapping and machine learning will evolve as well and it will be nice having the additional hardware that makes that facial mapping possible on both platforms.

As an example, take a look at this video, which shows off a deep neural network that allows you to change your hair color in real time. Imagine an app that does that for everything about you, swapping out glasses, facial hair, masks, colors, earrings, tattoos, what have you, all tightly tracked to your face.

Face ID on the Mac would allow macOS to keep up with iOS in this space. The question is, would Apple prefer this sort of technology to be available throughout the ecosystem, or would they prefer face tracking to be something that distinguishes iOS, a gentle nudge to move all users to iOS devices.