The measurements are of system firmware and bootloader stages + configuration. If you change any of those... Then, in the case of full drive encryption, you'll

The measurements are of system firmware and bootloader stages + configuration. If you change any of those... Then, in the case of full drive encryption, you'll be asked for the BitLocker recovery key at bootup. If you used Windows Hello for authentication, that option wouldn't be available - making you have to use your password instead to login.