This is unethical, basically he calls for jumping off of flights at layovers, which violates the terms of the ticket. There's even a security issue for the airlines, because they need to check if your bags are flying unaccompanied. Ironic that the NYT cracks down on people evading its paywall but is selling content on doing the same for air travel.
Note this is also possible if you check luggage: the airline is not obligated to let you get the luggage off the onward flight, but there's no airline that wants to carry baggage for a passenger who's not on the flight anymore (for security reasons).
If you're planning such a stunt (with baggage), try to have around 3 hours hop-time; else you WILL be delaying the onward flight with your luggage.
Layovers > 4 hours are considered as off-the-airport stopovers (domestically, US). That means the fare you'll get for SFO->DFW->BOS = SFO->DFW + DFW->BOS (made up routing). Exceptions: DEN for UA, ORD for AA, SEA and ORD for AS etc ("transit hubs", that is); where stopovers are free.