I believe that holding altcoin too long is very risky as you never know when the price of altcoin will crash and how long it will take its price to recover back so its good to sell them off when you are making good profits and buy them back when price drops and when it comes to bitcoins I prefer to hold it for a long term to make higher profits in future.
If you want to become rich in future then investing in right altcoin is the key to success as the growth of altcoin is too high in compare to bitcoins and with bitcoins you need to wait for a very long time to make huge profits from it and not all have that high level of patience to hold bitcoins for a very long term.
I agree that holding bitcoin for a long term can give us good profits but if you have enough bitcoins in your wallet then why not to use them in trading altcoins where the opportunity of making profits is even higher and quicker in compare to bitcoins so don't keep your bitcoins simply idle in your wallet.