God forbid we are ever in another emergency like an active shooter for example.
Being able to lineup and donate blood or having something that shows parimedics what your blood type is can be critical.
I've had five surgeries in the last eight months and I've received multiple blood transfusions yet for some reason blood type is not indicated anywhere on my health records.
I now have to book an appointment with my family doctor and explicitly request the test that determines your blood type, seems like an awful lot of hoops to jump through for what should be standard and readily available info. - Rant over.
EDIT: I'd donate blood if I could. Just had my leg amputated and can't drive yet