This practice was used frequently (and within airline rules) in the heyday of air travel (when there was real effort to give customer service) in the late 20th century. The airlines changed their rules to prevent customers from using the discounted prices designed only to high volume/hub cities to wreck the chance of airline profits on less popular intermediate routes. Running a competitive, profitable airline is a real challenge.

(Stating the obvious, one must not check any baggage in this case. )

It just seems anti-mercantilist, somehow. Once I purchase a product or service, I should be able to do with it as I please.

I think a cruise ship will allow a customer to leave a tour at the next port or any port along the way.

Capitalism does support the concept of contracting and pricing at levels that the market will bear.

Nothing will happen, but they will cancel your return flight.

If I miss my connecting by accident, what could they do? Do they charge me an additional fee for missing a flight?

And what do you do with the baggage you checked?

The logistics this produces is insane. We have optimized this pretty well. Usually you can buy the trip you want, and the price difference is usually minimal.

Back when we used a service, I was able to book some great trips. I had a layover in Houston, and I had the person make it an overnight stay so I could catch a BBQ place and check out Houston. It literally didn't cost me anything extra (outside of the meal and hotel), it got me back a day later...

Nowadays, I am in just too much of a hurry!

If you are going one way this approach might work. If you have to get back, you could be in a real world of hurt. the return would be from the booked destination not the local you disembarked at. Try showing yup with a ticket fra a to Z when you are in B. A few questions may arise from this effort. Just a cautionary note. for all inclined to try this approach to travel.

Iceland Air has stopovers in Iceland on the way to Europe. They let you schedule as long a stay in Iceland as you want at no additional cost. If you ever take them up on this, you'll find Iceland gets your money anyway. Iceland is expensive.

Regarding your question about charging more for one leg of a trip than two, it used to annoy me. One time my company flew me to part of a trip, and I wanted to use the return leg of another trip I had purchased. I found out you can't take the return trip without the outgoing trip. I was 25 y/o. I was incensed, and after arguing they gave me a decent deal.

These days I just accept it as a fact of life. The one time I flew private, I was amazed at how much easier it is, but it's much much more expensive. So I figure part of the price of flying commercial is the rules and rigmarole.

For those that are not allowed to disembark, this technique would not work. But, is a person trapped on the plane, even though others leave? How would the airline know who is disembarking?

Often, a person has to switch planes for the second leg, so they definitely disembark.

Does the airline allow any passengers to disembark there at all, or are they picking up passengers at the intermediate stop only?