If you were mining ETH back in Nov of last year with a six card rig you already and at a loss once power was factored in, you were able to a accumulate several ETH a week, more than you could have by buying ETH at the $8 low directly, for little additional risk other than your power cost. You came out way ahead once the market turned AND still have the hardware. That's why it's important to focus on mining as a long term hedge and not a daily profit center.