I am personally a miner, and I keep all I mine. I just sell from times to times what I need to pay for the electricity but that's all. Time said me I was right and with my predictions in the crypto-currency market, I will be right another time.
I likewise mine and keep but I do some selling in between; I'm into Altcoin mining and all I do is sell them into bitcoins and hold even though I loose some in moving the coins around until it lands in my Bitcoin wallet I think it is best to save than to sell for fiat.