I believe that it is not a good thing to sell everything at once because there is a possibility that you will regret it. There is a chance that the price still goes up after you sold everything so you lose money there.
Indeed, I think a lot of people if they sold it right now will regret it later because the profit will now be not much compared with the future.
Most likely you could make a lot more profits in a couple months because of the halving.
Yes if a person sell all his bitcoin after the halving there will be a lot of money to be taken because halving event is giving us so much profit and the value of bitcoin is going up.
There are now a lot of people that is holding their coins and that is because the value is not high enough to sell it with a nice profit and that is quite bad.
Many people see that the halving is coming but the most people are thinking that the value will not even rise in the halving, but you never know what can happen.
There is no reason to sell everything now but you can sell indeed now but not everything it is also smart if you are save some for later so you can that sell it later.
And that should be perfect if you can make more profit in the future, but you dont know when the time will be.
It depends, if you have purchased at lower price then current price then you should sell some of it, and rest keep for halving, and who knows if price drops before halving you can buy some more of them.