Earlier quoted context omitted.
Expiry date: It checks that you're not using an old card that someone has just thrown away, often card numbers remain the same if you get a new one. This is effectively just specifying the version of the card, and is something that needs to be on cards anyway (so the user knows when they're no longer valid). Additional benefit is that it means your customer has just checked that their card is still valid. CVV: Not su…
That doesn't seem convincing, for the expiry. The issuer needs to keep track of cancelled cards anyway, and they should be cancelling expired cards anyway - it seems like a huge security hole to keep expired cards in an active state and rely on an expiry date check to reject transactions. I assumed that it's a leftover from early days, before online card checks, so the merchant can check that the card is still valid…
I believe it's a convenience thing for the end user, when issuing a new card - offer a couple of days "grace" - and arguably there isn't much risk associated with this practice: lost/stolen cards are always cancelled immediately.