Hidden City Ticketing, it's been discussed many times here.

In short, the airline is only obligated to take you to your final destination, so if you booked say LAX-ORD-DTW and wanted to get off at ORD, and there were IRROPS for whatever reason, they have the right to book you LAX-IAH-DTW or etc.

In addition, the airline may zero your frequent flyer account, so that you lose your status, all miles, etc. It's not worth it for me, but if you want to take the chance, on an airline that you don't fly regularly, then by all means go for it. Just don't complain if you get sent somewhere other than your connecting city.

One more thing, don't check any bags if you are trying to do this. They'll get shipped to your final destination, and asking the GA to ticket it to your connecting city gives yourself away.