Open-jaw flights let you fly into one city and out of another, and most people never consider them because the search box quietly assumes you'll leave from wherever you landed. You don't have to. If you fly into Rome and your trip drifts down to Naples, you can book Rome in and Naples out instead of doubling back to catch your original return. Sometimes it's cheaper than a plain round trip. Sometimes it just saves you a wasted day of backtracking. Sometimes it's neither, and the ordinary round trip wins. The only way to know is to price it.
What an open-jaw ticket actually is
A standard round trip is A to B and back to A. An open-jaw keeps one of those legs and changes the other: you fly A to B, then come home from C instead of B. Most airline sites and search tools tuck this under a "multi-city" tab, even though you're still only taking two flights. It isn't two separate one-way tickets stapled together, and it usually prices better than buying two one-ways, because the airline still reads it as a single round trip with a gap in the middle.
The gap is the whole point. You cover the distance between B and C some other way, a train, a cheap regional hop, a rental car, and you skip paying to fly back to where you started just to leave again.
When open-jaw flights actually save you money
Two cases. The first is a trip that's already a loop: you land in one place, wander, and end up somewhere else. Backtracking to the original airport costs you time and often a pricey same-day fare. The second is when the return out of city C simply happens to be cheaper than the return out of city B. Fares aren't symmetric. The flight home from a smaller, quieter airport can undercut the busy hub you flew into, the same way a nearby airport can beat your home one.
Do the honest total, though. Add the cost of getting from B to C. A $60 open-jaw saving that needs a $90 train isn't a saving, it's a $30 tax on feeling clever. This is the same math as letting your dates flex: the shape of the trip is a lever, not a magic trick, and it only counts once everything is added up.
What we do, and what we don't
We're not going to plan your ground route between cities, because that's your trip, not ours. What we do is watch the real fares on the routes you save and send the best ones each morning, round trip or otherwise. If an open-jaw is the shape your trip actually wants, price it against the plain round trip and let the total decide, not the habit of leaving from where you landed.