Taking profits at the right time is good, but I think for some quality altcoins with use-case are good to hold in the long-term.
Well if the altcoins has some bounty campaign then you should think about holding it. Im not saying that some of them will not pursue in the long term but most altcoin suffer a great deal of loss and end up dying and failure always happened on their end.
HOLD long term
Long-term HOLD is mainly applied to investing in long-term projects / coins that you really trust. You can buy and wait until the market is saturated, as well as the market to make things clearer
One example of it is ethereum. I dont mind holding my altcoin ethereum for a very long time as we see how dedicated this project for a very long time. I think not all have this kind of seriousness and dedication. Most altcoins I have noticed are all dead but only those retained have listed on major exchanges such as npxs. See the price now and you would hurt a bit if you invest on it on the midst of 2017.