A good example is one way international flights (eg. as part of a DIY round the world trip), where the cash one way fare is astronomical.
Eg LHR-JFK oneway can be over A$4K (yes - in Y!) flying oneworld, yet a return fare can cost less than A$900.
HNL-SYD is another example, but not quite to that extreme.
These are both day flights so many might find Y OK, and/or in the case of HNL-SYD, it's very hard to get J seats.
