Originally Posted by
BThumme
I think that point gets overlooked in this thread. You are doing UA a favor by SDC'ing. You are moving onto seats they weren't able to sell and making room in the future in case anything happens for other passengers down the line. Sure, there are a couple times where it may hurt UA and backfire, but that is so minute and unpredictable (and for a relatively low cost to UA) that I'm surprised more airlines don't offer this.
Not sure that is such an easy conclusion to draw.
SDC can be used to move up a flight or to move out a flight and you can SDC to a flight with more or less open seats than your present flight, it is probably more wash on load balancing -- only UA knows if it frees up more valuable space or not.
My guess, UA viewed this as a competitive benefit with no real cost to UA and it might cut down on the number of business travelers that were booking multiple same-day flight options (which did have a really negative impact on UA's load management).
And as long as the SDC abuses are minimal, UA tolerates it for the benefits (whatever those may be to UA).