The problem is, you can never change it. Ever. You can change your mail, you social media accounts. You can even change your phone number. Changing your iris or eyeball is another story, well if you don't want to get blind, at least. This is the case for all biometrically relevant data. Now, that means, that it doesn't need a purpose now. It does not need one tomorrow. It will follow you around your entire life, until at some point, tomorrow, in 1 year or in 30 years, there will be some huge thing that will fuck up your life based on something you said, did or whatever & it will be proven that you did, said or whatever it, because they have your biometric data. For fingerprint scans, you need to touch something. For eyeball scans, you literally just need to look around & accidentally look in the wrong camera lens.