Minecraft wiki entry for Things_not_to_do, associated text: If playing on a PC, holding Shift while crafting items crafts as many of that particular item as possible. If the player does this accidentally, they can end up wasting a lot of resources unnecessarily. For example, if the player has a lot of diamonds to craft a full set of diamond armor and they accidentally craft 10 diamond boots, the player would have wasted a large amount of diamonds on armor they don't need.