Theoretically, someone buys a bunch of miners and sets them up somewhere and sells the rights to the income from the miners to others, and takes an operating fee for maintaining the hardware. Then, if that person sets up an exchange to trade the GH for mining, which is really ownership of the rights for the rights to the mining income for that amount of GH, and takes a %age of each trade, then you have what bit-mining.co tried to be.

The advantage is that you do not have to buy hardware and you can mine. The disadvantage we have seen in what just happened.