Lets say you buy something from the marketplace. Then later someone has a code giveaway, but they don't say what the code is for. You go to redeem the code, and it's for that something you already bought. What happens? Does it not use the code? Can you then give the code to someone else? --- Movies that I believe will come true: Wall-E, Idiocracy Halo 1 > all other Halo games
If you redeem a code through Xbox.com it automatically redeems the code and if you have it already, you'll just download it again and invalidate the code. If you go to 'redeem code' through the Xbox Dashboard, you can type in the code, then it will bring up the screen telling you what the code entitles you to and a button to download it. As long as you back out of that screen once you see what the code is for and don't hit 'download now', you or someone else can still use the code later.