Flesh420.613: I know you can use the keycard for the vault later, but it'd be cool if there's a rare chance of a floor generating with an indestructable locked door that requires a keycard. Maybe a really low chance, and inside the room something useful might spawn—7.62 rifle in an early level for example. The room would carry a hefty risk for a decent reward though, so maybe if you're not prepared it may be wiser just to skip it.