I think trading can be an advantage to the person that doesn't have a lot of money into a game. Let's say I bought a game for $1500 years ago that now sells for $3000. If I can trade it for a game that's worth $3000 then it may seem like I've gotten the better end of the deal as I only have $1500 into the game.
I realize that I could sell the game for $3000 and then buy another $3000 game but by doing that I lose my profit or equity that I had in the game. If I can trade it then my intial investment of $1500 continues to bring me profit in the form of games that are worth more than what I have invested.
When I'm ready, I can sell the game for what it's worth and realize that profit.
Until then, I can keep trading games with a minimal investment with no additional cash outlay required by me.
Having said that, I will say that I've never traded games yet.
Dave