How would an asteroid affect the economy?

The economy would benefit from having an asteroid orbiting the earth, asteroid mining would be a breeze if the asteroid was in orbit around earth, there are some asteroid with lots of minerals that could be mined and refined and sent to earth for sale and that would have a small effect on earths economy, after all earth is getting short on gasoline not minerals and ores. Now the economy would be shattered if the earth was hit by a asteroid, most likely independent kingdoms and small feudal nations would arise and implement there own system of currency or legal tender, there would also still be a lot of trading posts in the rural area's where the barter system would be used, mind you this is if there are people who survive the asteroid strike.