Say you made 10000 in 2017 and purchase gear late in the year.
The entire gain of 10000 can be sunk into inventory if you resell used gear.
You then sell the gpus at peak prices in Jan of 2018. The gain is this year and you can offset with a mining loss.
Yeah, you were right. But I'm not doing this, Q1 2018 is a pretty good moment for mining (at least for me), so I don't even think to sell my gear. Maybe I'll do this next time (I Just need to know the moment). Good idea!
Really just depends on the true reason you mine. If you are mining and selling immediately then you are most likely not making money. I have been mining for about a year and still do it because I believe in crypto and mine coins with solid fundamentals that I believe will go up in value and then I will take my profits.
For some miners maybe yes (most miners do that), but I've never held the coins, I need to pay all the bill (at least once a month) but I still get some profit after bill payment.