If you are answering to my Berlin->Györ example:

Yes, it is not exactly the same thing but the point is: by getting off at B you are making the B->C flight travel with a wasted (empty) seat. Which they would have preferred to either sell to someone else or use for moving a pilot or technician to C.

(Note also that this trick of getting out mid-itinerary only works if you do not have checked baggage, because that will arrive in C, and neither the airline nor the airport will be happy to reroute it to wherever you thing you want to go next.

Flying is expensive and logistically complex. Just making sure you end up where your ticket say is complicated. If you (as a customer) decide to change your plans you are making everything more complicated (and possibly preventing other customers to pay for the whole itinerary).