What you might not realize is that, with DL at least, this stopover provision is also allowed on international itineraries. You may stop either in the US or internationally en route to your final destination (stop only in one direction or have an open jaw, but not both). It can be a great benefit, as can redeeming awards for domestic travel. Think last-minute emergency travel, travel from remote airports (often much more expensive because of little or no competition), and travel to places like Alaska from much of the lower 48. As you said, it depends on who you ask.