It mostly depends upon the coin behavior and the your trading strategies, how much you had invested at the moment? Secondly in what ways you are doing trading? And another way of taking profit is that profit should always be at some percentage, it is not necessary that it must be 50% but it should be profit, whether a big profit or even a small one.
I agree with you, taking 50% profit is too high on the spot market and investing up to 50% profit may take a long time. So analysis is needed.