I had assumed that buying round-trip plane tickets saves a lot of money, but lately I've been comparing prices and the round-trips I've seen are almost identical in price to just buying two one-way tickets separately.
If round-trip tickets are just supposed to be more convenient, then that benefit surely seems outweighed by the flexibility that one-way tickets give you. Not only is it easier to choose different airports for your outbound and inbound flights, but you can avoid the usual traps if you want to change something later on. I've been in situations where I've needed to change just the outbound flight and the cheapest option was to just buy a new one-way ticket but I couldn't do that because the rigidity of the round-trip ticket prevented a traveler from boarding a return flight if they didn't board the outbound flight. With a round-trip ticket, the whole thing counts as one. If you want to make one little change to one leg of one flight and you can't do it, the whole ticket is wasted. (In the same vein, it seems you also get less flexibility and almost no benefit from putting multiple passengers on the same ticket.)
So my question is this. Is convenience and a marginal (perhaps even only perceived) cost difference the only benefit to a round-trip ticket? Or is there some other purpose I'm not aware of?
EDIT Nov 3: I apologize for not considering international travel. It's been many years since I've flown outside of the US.