Recently I also regretted not trying much harder to print a hard copy of my boarding pass when I checked in. I was "vipered" (automatically rebooked) off of a flight for which I had a confirmed seat and had already checked in. This apparently happened when I was on the way to the airport; I was placed in horrible flights the next day when my confirmed flight posted an additional ten minute delay. If I had paid my hotel's business center to print the boarding pass (their executive lounge was closed for the weekend), I would have been able to get through TSA security and probably fix things in time in the lounge or at the gate.

Instead, I was forced to wait over an hour to see the only agent working the SkyPriority line so that it was too late to put me back on my flight. When I got to the gate, the GA refused to add me to the standby list because it wouldn't be "fair" to those already on the list. [I had a paid FC ticket in this case and there were obviously going to be a lot of passengers missing the flight due to the extremely long lines to check in and drop bags.]