You can only imagine the pain of having a "-" in your last name, when some documents accept spaces but not hyphens, and some accept hyphens but not spaces, and some accept neither, and some require other identifying documents to match each other...

I imagine this is the sort of thing that makes these stay so open. If my flight is cancelled and rebooked with a partner, but my id says "Last-Name" and my boarding pass says "LastName" and for some reason I'm in the system as just "Name," then it's really nice the I can still make it on my next flight departing in 10 minutes.