They aren't necessary and you should be able to learn the basics within the first few moments of playing the game. It is also better for the environment.
Oh whatever. The environment is hurt by cars, clothes, houses, food, etc not instruction manuals of all things. There is a place in the case for it anyways, why would you throw it away? Its a trendy excuse to get out putting in the effort. I will concede that its inevitable, though. It's not that you NEED the manual to know how to play. Its just a nice detail by the publisher that shows that he/she cares about the experience being offered to the consumer.