To provide the Android hardware-backed keystore [1]
If it's present, this is used by apps like 'Google Authenticator' and 'Symantec Vip access' to store credentials in such a way that they can't be copied off the device or backed up.
When this technology works perfectly, the idea is if you have a short passcode and someone steals your phone, they can't extract the encrypted data and brute-force the passcode without an electron microscope and a team of engineers.
Unfortunately, it can also be used for user-hostile applications like providing DRM and preventing backups and rooting.