Everything will depend on the situation. For example, you mine to earn a living and in this case you need money all the time, in this case it does not matter what price the main thing is to sell ETH and get money for life. On the other hand, you just want to maximize the profit from mining ETH, then you better keep ETH from selling and wait until the price reaps the highest possible result. Of course, this is a risk, but this is the whole interest to get a double benefit, the first from mining, the second from the rise in the price of ETH.