Originally Posted by
klausa
It has to be encoded in the bar code anyway, so if someone wants to actually mess with your reservation, the only thing you’ve did is delayed them by about seven seconds.
Originally Posted by
WorldLux
Without the PRN, you'd still be able to retrieve the ticket with the e-ticket number printed on most boarding passes. Personally, I don't see that much of an issue with having that information printed on a boarding pass or a bag tag. The best advice is to not share pictures of your boarding pass online (seems obvious, yet thousands do just that) and to remove the bag tag once you're reunited with your bags and keep them until you can properly dispose of them.
Casual snooping (out of nosiness) is easier to prevent if it's not printed (even though it's in the bar code), and ticket number is harder to quickly type in.
Really, there should be an extra step to get into MMB such as needing to enter a piece of information that is only likely to be known to someone seeking to access it legitimately.
No idea about the Blue card expiry date, as I can't even find it.