Depends on your money in this moment. When you have nothing to eat better to sell your coins you know
In other cases just look for profit it comes with experience.
No, you should sell your coin mined when you have chance to sell it at good price. Example you waited a long time to sell your coin at high price when the price of which coin you mined just decreases everyday. And someday, you need money for urgent case, it makes you must to sell your coin at lower price instead of the time you can sell that coin at higher price many much at this time.
Yes we should sell it earlier when the price are high, don't be greedy because sometimes the more you are waiting for a high price the more the coins price become low that makes you loss if you sell it. When you want to hold it you should longer your patience so that you didn't missed any opportunity in the future to earn a bigger profit.
According to my experience, if you want to save (hold) coin from mining, you can just do that when the market has bullish trend, like the last year, you can hold Ethereum, Dash, Monero, Litecoin or even Bitcoin mined to have better price for selling. But currently, hold coin from mining just make you have more losses. Sell it for the current market, because we are staying in a big bearish trend.