To me it doesn't make sense for AC to deny standby on an earlier flight, because if the next flight goes mechanical it is one less passenger to worry about.

This thread comes to me as a surprise. I have never been denied standby on a previous flight unless it was full. On average I do this three or four times a year with AC.

Actually, if AC manages to finish its business with me sooner, I should get a rebate like I give my customers in these circumstances.