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.
Selling everything now around this time is not that bad because as you can see now you see that the value of Bitcoin is not even rising and it is also not that low.
But if you are for sure that the value will rise of Bitcoin than you can better wait indeed until the value will be more in the future so you can also get some more profit.
The hard thing is that you never know it from before and that is the problem, maybe it can also reduce in the future.