I've always wondered how often people really use HCT. I would think that many of the potential uses are limited; that is they are too far away to be practical. Certainly you could do a one-way positioning flight and then get off early on the return leg, but I'm not sure how many people really do that (examples in this thread show that there are times that this will ultimately save money). There are clearly enough that UA feels the need to send a warning shot across their bow. About the only times I have dropped the last segment of an itinerary were when I had business trips come up at the end of a personal trip and it made more sense to use the connecting city on the return as the initial city on the outbound. The last time I did this, I did go to the gate and tell the GA that I wasn't going to take the flight and that my plans had changed due to business.

It is also fairly clear from this thread (and others before it) that not everyone understands what HCT truly is.