I remember one time connecting in to Vancouver and asking if I could could jump on the earlier flight rather than waiting 3 hours. Done this multiple times with US carriers if there is room. What do they care if the seat would have been empty otherwise?
I was informed by the AC agent that there would be a $175 fee for the ticket change. Plenty of other examples of rigidly following the rules even though it cost them nothing.
Good point. I'll keep that in mind the next time!
If you had asked to standby for the earlier flight, you would almost certainly have been told "ok we've put you on the list; check at the gate" with no charge.
It might depend on how (over)sold the flights are. If your original flight is oversold and the other one is not, it seems like a win-win situation.