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.