I also had to pick up my CX LAX-HKG BP at TBIT. Maybe it's just to make the whole OLCI experience more consistent.

I often fly on American (out of DFW Airport), and print out my boarding pass. However once I get to the airport, I do go up to one of the self-service kiosks to check in again .... why?

I like that last minute opportunity to better my seat; people may have gotten their upgrades and have now vacated an aisle seat better than what I have (i.e. closer to front).

OR, depending on factors that I don't understand, I may be offered a 1st class upgrade for extra $$$. For example, yesterday I flew back to Dallas from Boston. At Logan Airport I check in at self-serve kiosk and an offer pops up to upgrade to 1st class for an additional $180 (I'd purchased the roundtrip DFW/BOS ticket for $289). I was feeling stressed from this trip (a family visit) and so, the opportunity to sit at the front of the bus sounded mighty fine to me.