Note to everyone: You can sell them for money which you can use again to buy steam games or ingame stuff (ie. for dota 2 or whatever).
I sold some cards and made easy 5€. 
If you collect a whole set of cards, its even easier money. And you can collect every card again by playing.
I've looked at nearly every game that has cards, and almost 90% of the games are selling the cards on the market for a profit of .12 cents(in beta cards were selling for a ton, but since the release of this to the public the prices have shot into the ground). Thats it, lets say you have as many games with cards as i do( i own 20 games which have cards), which means i was given a total of 84 cards possible to sell, if i actually play all 20 games to receive them all. Each card selling for say averaging .14 cents, which steam takes .2 cents of anyways will leave you with a grand total of $10.00 give or take probably a couple of dollars. Considering that some of the cards sell for as little as .09( which dont forget steam takes their .2 cents) can vary the money you could earn above.
Also these cards do not ever return, you cannot earn more of them, unless you are granted a booster pack, giving you a whopping 3 cards, which can be sold for .36 cents or so, unless you sell the booster itself making a dollar. However the chances of receiving a booster is next to shit, as you must have a incredibly high steam level(level 50) to actually make these on a good basis.
TL;DR Either way, you arent goin to be quiting your day job to make a living selling steam cards, and your goin to make like .30 cents, can i have your cards, or trade for em?
