I do hold only considering that the market may not fall further. If it continue falling than better to sell the coins and later buy at the lowest price and make some profits in between. Like at present it is a short fall so hold is a better option.
Holding is the right pick, but here to risk is there. I understood it recently after investing into an alternative that was increasing regularly. At some point the price started falling, but I had the hope that it'll increase again. All of the sudden the coin was no more available in the exchange. By such instance we can't do anything just accept the loss.
There is absolutely no level of trading that does not have its own risk, how to manage those risk is what makes a trader good. Just like you said, as much as Altcoins were having a pretty good boom, all of a sudden, we started seeing huge reds on most of them and some even dropped so low that their ability to recover would take some months.
This is what every trader should always expect even though it does not seem like something that could happen at that moment. You know the limit to the loss you can have, set a stop loss and know either you lose this or you win this. Sometimes holding for too long, most especially some shit coins can be bad for the health of your trade.