It could be good to hold your bitcoins for a long term, keep in mind there are more risks that you have to take to do this but it will also maybe be more profitable at the end, A long term investment can let you gain a lot of money if the bitcoin grows to a very large currency.
Someone can surely gain a lot of money by holding the funds for too long, but on the other hand he may also lose a lot of money by holding them for too much, because no one can know if what happens tomorrow so it is never guaranteed if the price will grow or it will come down, that is why it is always better to sell a half of them when you see a reasonable price, and keep the other half and if you see price coming down then sell the second half to stay safe from losing profits.