I've always thought that it's necessary to take some losses as then you will be more careful with timing of the sells... basically one must remember the amount and price that one has bought and then sell when there is enough profits, not when the cryptocurrency is overbought.

On the other hand, one should always buy when the cryptocurrency is oversold, no matter what the exchange rate is.

The general rule is to never sell or cash out more than 50% of the total value of the portfolio.