Originally Posted by
tdracer
Triploss, it's not as common as it used to be, but I've run into cases where a one way ticket was actually more than a round trip. About 25 years ago, I was leaving on an extended overseas assignment, so I was going to drive my car to my parents house in Colorado to store and fly back home. It was cheaper to buy the round trip ticket and leave the second half unused than to buy one-way.
Indeed - and both in Europe short-haul and TATL long-haul, round-trip tickets are almost always cheaper. That may have been the case a long time ago as you say, and it's still very much the case these days.
But that doesn't mean that the return has zero or minimal value. You're still buying two journeys on one ticket - they simply will refuse to sell you a cheap outward journey unless you also pay for the cheap return journey, but that means the ticket is constructed as something 2x300 GBP (not 598 GBP plus 2 GBP). That 300 GBP fare 1-way fare has a condition attached, which is: must be ticketed together with a return journey (that return journey will happen to be available at a similar price). You can find 1-way fares without the return condition... but they just cost a lot more.
It may not seem logical from the outside perspective, and it does seem like they're giving you an effectively free return - but the underlying construction is fares for each journey, which may have the requirement to be part of a round-trip ticket (cheaper) or not (more expensive). Just like they can have requirements around having e.g. 6 days between outbound and inbound (cheaper), or no requirement (more expensive). Or refundable (more expensive), non-refundable but rebookable for a free (less expensive), and sometimes completely non-changeable (even cheaper). Similar reason why Milan-Zurich-SFO might be cheaper than Zurich-SFO even though you sit on the same long Zurich-SFO flight. All around optimising what you can pay.
And if you buy a lot of returns where the return isn't used, expect your travel agent or employer to be contacted for some extra cash. But that's only a risk for very frequent travellers...