Autofilling when buying online, having the details handy/ready to be copied if autofill is not an option, keeping track of them in a single place while being encrypted together with other personal info... To me the benefits are many!
Thats cool but also so unusual for me. You just don't add card details at all here, and if you do, you just trust that service and save it permanently.
If someone is actual heavy card user, he will have temporary/shortlived cards anyway.
