Its really important to never sell your entire stack of coins, you never know when the price will stop going up. I made this mistake before and sold bitcoin way too early only to watch it soar to the moon. You better believe I aint making that mistake again.
i think it's depend on the condition, if the market of the coins is not good anymore and keep going down, it's better to jus sell all your coins before the price keep going down and down. but if it's only going down a bit, find out what is the reason, and if the reason is only small then just keep holding.