If you want to grow them then you need to take help from trading, holding them is good but eventually it will not increase the number of coins in your wallet, but with trading you can expect that.
Whereas trading bitcoin will give you more benefit on daily basis, still it will have many risk associated with it, but it will give you chances to develop your skills so that you could minimize risks when gaining experience.
The only risk in holding them is that you may suffer loss if price falls in future, but that is unlikely to happen as we may witness some best and higher price in future.
People prefer to hold their coins for long term but they ignore the fact that they might suffer losses if price falls in future as we cannot be sure that price will surely go higher in future.