There person say you should hold is rather preventing you from losing your asset by selling them cheap now since there is a potential gain from holding in case there is a breakout in the market and things turn upward.
It all depends on individual financial needs because if you have invested your spare funds and not in a hurry to withdraw those funds and believe in cryptos then you can hold them for long. Also if you can buy some more in dips to average down your buy price but some people might have invested borrowed money. Those kinds of people should fix target price before buying for both losses and profit. Once they reach those targets just sell and wait for right time to enter the market again.