If you wish to hold some coin then use exchange only for during exchange. Just exchange your coin and transfer on your personal wallet that you have controlled. Specially you can use hardware wallet.
Because many exchange hacked buy hacker. Many people loss their capital by hack.
So please don't hold your coin on exchange for long time.
Probably its a great advice. Its better to be safe than losing your money. We have to be more secure if we can save in our personal wallet.
This is not even a matter of probability as this is more of something that should be taken note of. Exchanges are centralized and if anything happens to them in a negative way, same thing happens to the user's fund which is the main reason why it is very important not to leave all that one has on the exchange to trade with or to hold. There are wallets that are decentralized which gives control of one's keys and they are far better when it comes to security of your assets.