I don't really see why this is such a big deal - you still have to go to where the ticket originates in order to start the journey. I anticipate the airlines policing valid usage of the first coupon even more strongly.

But that's about all - it doesn't stop airlines have a different price for journeys starting in Warsaw or Lisbon if that's what they want, all it means is that you can have the ticket more easily in your hand in your home country before making the trip to Warsaw/Lisbon to start the ticketed journey. This has never bothered me particularly - I have started a number of ONEs when only in transit at the originating airport having arranged pick-up on departure from the airline or TA (BA or AA in CAI multiple times, CX in CDG, Amex in TPE) and it has never been a problem.

There might be some small financial gain in that you can play the exchange rates and take whichever of your credit card or the ticketing system gives you the best one - that could be worth 2 or 3% I guess.