The fingerprinting is done to ensure that you are you now. It may seem silly because you know you're you, but that's the way it's done.
Every time someone is booked into a police station new prints are done to ensure they are when the incident occurs.
Every time someone applies for a security clearance from the government, prints are taken for the same reason. And taken again when the clearance is renewed.
If you were in Georgia, they'd be taken every few years when you re-applied for your Georgia Weapons License.