1. The reason Romans invaded and conquered Britan was its abundance of natural resources, especially metal. The author clearly states this as he also states that Britons did mine the metals but not really efficiently. They did not have the technology to exploit the mines to their full potential. Romans with their technology were able to do just that.
2. For Romans, of course this meant that they can now produce the things they needed on much larger scale thanks to the resources provided by their newly conquered territory. Thus as the text states, they used the resources to craft metal coins, tools and numerous weapons that would be used all over the Roman Empire.
