I won a helmet and wanted the chest piece (with a 12% drop rate) to go with it, but I wasn't allowed to Need on them because the Tank wanted it. Eternal sadness.
Well there's Need and Greed. Greed is for when you don't really mind if you get it or not, or if you can't Need. Need is used when you HAVE TO HAVE IT, either due to the rarity of the item, or because it's an upgrade for another item.