Hong Kong Bitcoin miners pour data centre in a fish tank

Working out how much this will cost in electricity per hour, and factoring the cost of the hardware is easy enough. Unfortunately, the value of bitcoin is so volatile, and the algorithms to mine new coins gets increasingly difficult (though I believe the latter is reactionary to the evolution of technology, and the number of people employed in mining, so it's not possible to predict). Therefore, there's no way of estimating, or guaranteeing when, or indeed if you'll ever get your money back.

I could see bitcoin mining installed in place of electrical heating (radiators, swimming pools, etc), then you could argue that the energy is being put to better use than heating a resistive element....

Bitcoins? What am I supposed to do with these?

I realise I am about to proclaim myself a drooling Luddite ignoramus, but what exactly in God's green earth are you supposed to do with Bitcoins?

I can't use Bitcoins to purchase fruit and veg at the market. I can't use them to pay for fuel and maintenance for my motorbike. My utility co-op will not let me pay my 'leccy bill with Bitcoins. The alphabet soup government agencies take a dim view of buying consumables off of Silk Road. I do not have any ransomware on my computers that needs unlocking. It does not appear that any of the "specialist exotic filmography" websites accept Bitcoins for membership fees. What is left?

Do I collect them in a little box so as to increase the length and girth of my e-willy bragging rights? What exactly do people do with the bloody things?