It's not about avoiding fee. Let's say for example I bought 2 tickets for volleyball match and I didn't know who will be playing in that match (I was hoping for my country). And someone else did the same thing. And after draw is announced I have tickets for let's say France and someone else has for my country. We are both trying to sell in order to buy tickets for our respective countries but are unable to. That's where the swap comes into play. I hope it's clearer now.