To horde or not to horde
At this point in the maturity of the Steam Marketplace, it is possible to earn a ton of items for doing literally nothing. Trading cards are earned simply by spending time with a game window open, and many in game items like TF2 hats are earned the same way. As the free virtual shiny objects begin to crowd your inventory, you’ll need to decide whether you want to cash them in, or stack them high and covetously protect them. For my own part I tend to keep them for games I like, so that I can craft badges and get other virtual schwag for that game – but I cash them in for the games which I’m not as invested in.
Pro Tip When considering to sell Trading Cards, take a minute to consider the opportunity cost of holding on to them. For very popular or free games like TF2, the cards trade near the basement price of around $0.07, limited by the transaction prices of Valve to net you $0.01. Cards for these types of games are worth very little, but when combined into badges during sales, they will net you additional loot which has a chance of being worth more. This means it is sometimes more profitable to buy or better yet trade to get a few cards to complete a set before a sale, and then craft the badge during the sale.