[mikeash]

I see two potential problems.

First, you probably shouldn't do this as the first part of a roundtrip ticket, as the airline can cancel your return if they think you're abusing the system. That may not be important for many people, but it's there.

Second, if something goes wrong (bad weather, can't find a pilot, whatever) the airline may reroute you through a different city, completely screwing up your plan. They don't really care where you connect, and as far as they know neither do you. If you book, say, JFK->LAX->SFO and the engine falls off your JFK->LAX plane while sitting at the gate, they might move you to a route like JFK->ORD->SFO, and saying, "but, but, I was going to leave the airport at LAX and skip my flight to SFO" is probably not going to get much sympathy from the agent.

[rhino369]

Third,

the overhead compartments are full and you have to check your bag.

[giarc]

Just be first in line to board the plane.

[mikeash]

Don't they give it back to you at the end of the flight when that happens? In my experience, only bags checked during checkin get routed through connections.

[Dawenster]

Very true, my co-founder discovered this the hard way.

A note on the roundtrip booking - correct, you should never book roundtrip. Your roundtrip should be made up from two one-way bookings.

[AKhoo]

lol I am the aforementioned co-founder. This is definitely a flight booking hack with costs and benefits that have to be weighed. I don't personally book this way for savings of just 10-20 bucks. When it's something like $80 in savings or more (I saved >30% on my last flight), you start to think maybe the expected value will come out positive, even with all risks considered.