It
is used for the iTunes Store and Mac App Store.
The only time Touch ID isn't used in Apple's own software is:
- The first login after a reboot, so as to protect your fingerprint data from hacking (logging in unlocks the Secure Enclave).
- When accessing any part of the System Preferences that impacts upon security and privacy settings.
The reason for this is the security hierarchy is first (and most important) your password, and second your fingerprint.
It has to be this way, otherwise what happens if your Touch ID sensor breaks? Or you cut your finger? You'd be locked out of your own computer.
So, anything that deals with a higher tier of security than Touch ID (this broadly can be defined as any part of the system that has the authority to add, remove, or change your Touch ID settings, for example the Touch ID pane and Security & Privacy pane in System Preferences) must have your password - the highest security clearance - to be altered.
These are the only exception that I've discovered. Everything else in macOS you can use your fingerprint for.