It is never a good thing to sell all your coins at once if you because there is always a chance that the price is going to still rise.
If you have then sold everything then you just missed out on some money.
Don't put all eggs in one basket, price can also get lower but if the amount of the bitcoin volume is low then the loss isn't much to care about because you risked that money and are able still to sell them so you don't lose 100%
Its always better to sell them in parts as future will allow you to make huge profits if price goes higher so selling everything is never recommended.