It enables the following:
- less liability for the merchant
- either the transaction was explicitly approved or wasn't
- sense of security for the user
- card never leaves you
- if you ever lose the card it doesn't matter
- there's no reason to sign anymore (less opportunities for fraud)
I can't quite put my finger on it but it does change the dynamic between wait staff & consumers when you're out dining - it just makes things simpler & you have to wait a lot less when you decide to leave.