Originally Posted by
ralfp
If checkin before t-24 hours is not allowed for reasons of "security", why are airlines allowed to issue boarding passes for flights > 24 hours in advance (connections)?

I know of no US airlines that issue BP's 24 hours prior to departure of the first flight-leg of the itinerary. (Issue BP=OLCI). Again, I believe this is limited by TSA.
After all, the TSA crack ID checker would never catch the wrong date, and then you'd be free to enter the sterile area, and reap havoc/meet some one at the gate/buy an overpriced airport soda/well, you get the drift.