Yes, it does, for some values of security. Operated correctly it allows you to know you can trust everything on your system from the UEFI firmware down, because if any part of that chain didn't match what you were expecting to be there the next step in the chain would refuse to execute.

Most people experience this via Windows, which automatically sets up that chain of trust so that you can know you've not had a rootkit injected somewhere. In other cases it may be Linux or something more exotic booting, and it requires some management by whoever is operating the device, but that comes with the benefit of knowing that if one of our devices has got to the point of decrypting it's storage we can be reasonably confident that it hasn't been tampered with, and so we can trust it to send good data.