Why mine asteroids?

Simply put, there is an incredible amount of wealth to be found in the asteroid belt. Many thousands of times the Earth's entire GDP could be gained from mining the asteroid belt. By mining in space we will also allow ourselves to expand the Earth's economy exponentially. To a point where we have moved to a post-scarcity economy with Rare-Earth minerals and Platinum group metals, even Gold being abundant and resultingly, cheaper. By comparing 3 different types of asteroids we can gain a much better understanding of exactly what each contains and the benefits of their size and composition.