Also keep in mind delta has no obligation to fly you to your first airport.
Say you're flying nrt-atl-stl with the intention of getting off at atl and missing the flight to St. Louis. If your Tokyo to Atlanta flight is delayed or cancelled delta could easily reroute you via another airport. They may choose to send you via Detroit and then you'll need to find your own way back to Atlanta.
They likely wont fine you or cancel your slymiles accoint but the above seems a lot riskier to me.