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.
I agree I would also not sell everything at once because it is better to always save some of your bitcoin for the future prices to come.
That is when you are going to make money but if you sell them all you will have nothing left.
It will be a worst decision to make to sell all our coins at a single point, as it can give us higher profits in future if we have managed to save some coins for that point.