Here’s one way it goes wrong.
I’m booking travel to a client I visit on a regular basis. Round-trip airfare has been about $450 since I first started working with them. This time, though, Delta.com quotes $1,300 for the same trip, or $900 with one connecting flight.
I call a live human being who confirms the new rate, and, after doing some checking, explains that Delta no longer provides a round-trip rate for this destination unless I stay over a Saturday. Otherwise I’m paying for two one-way tickets.
I figure it’s an oversight.