What does the TouchID button do on the new MacBook Pro?

In addition to TouchID functionality and serving as a power button, you can also configure the button to act as an accessibility shortcut. Just look under Accessibility in the System Preferences!

Shortcuts include things like Zoom, Color Inversion, Mouse Keys and more.

Seems the only function of the "Press" on the Touch ID button is to force shut down (after holding for 6 seconds). Kind of a bummer if you ask me.

https://support.apple.com/en-us/HT207054

Unlike with older Mac notebooks, holding down Touch ID on your MacBook Pro or MacBook Air doesn't display a dialog with options to Sleep, Restart, or Shut Down. You can find these options in the Apple menu. If your Mac is unresponsive, you can hold down Touch ID for six seconds to force a shut down. Note that you'll lose any unsaved work if you do this.

Pressing Touch ID won’t put your Mac to sleep. Instead, choose Apple menu  > Sleep. If your Mac has a Touch Bar, you can also add a Sleep button to the Control Strip:

Click Finder. Select View > Customize Touch Bar. Touch the Control Strip region of the Touch Bar to switch to Control Strip customization.
Use

You can do multiple things with TouchID on a MacBook, it's essentially the same thing as on the iPhone.

With TouchID you can:

• Turn on, restart, sleep and shutdown the system.
• Unlock and log in when waking your Mac from sleep. You must type in your password after start up, restarting, or logging out of your account
• Gain access to password protected sections, such as in System Preferences.
• Make purchases in the iTunes Store, App Store or iBooks store.
• Making purchases with Apple Pay in Safari

Although 2017 MacBooks start when you open the lid, the finger print button also acts as a power button, like all other laptops. You can hold it down to force shutdown and restart the OS.

I'm sure there is also more things that I'm unaware of.