There is a not-totally-remote scenario in which it is much better to book one-ways.

Assume you are flying A-B-A, and at the time you buy it each leg is $200.

The day before you are to fly A-B, your long-lost (sibling/cousin/child/dog/etc.) shows up and you want to change your outbound flight. By now the prices for each leg have gone to $400. You are willing to pay the extra $200.

When you go to change your A-B-A trip, because of course if you don't show up for the ticketed A-B segment the return will be cancelled, you are told that any change will cause the entire trip to be repriced. Your $200 return will now cost $400. Whereas, if it was a one-way, you could keep it for $200.