I beg to disagree, as far as I know we can hold the coins or Bitcoin for along time but not selling it ever, that is ridiculous. The essence of waiting will become useless.
You have the point and this is opportunity that we can make a good profit everytime the price is increasing since the price of bitcoin is unpredictable and we do not know when bitcoin will down or up again.. so to be safe you can sell partial of your bitcoin holdings.. from 15% to 25% depends how much you are holding just to safe your profit and not losing your opportunity..
I think that the main purpose of not selling bitcoin is to limit the supply of available coins.
That is good for everybody who owns bitcoins. Of course, not selling it ever makes no sense.
And then you have to think about about the fact that bitcoin is a payment system as well that has to be used.
Otherwise companies might turn their back on bitcoin.
I would say use it as often as you can, but have some savings as well.