It is not suggested to keep or store your coins on any exchanges sir. They might shutdown their platform at any time and your coin is at risk. Its better to keep your coins or tokens on a wallet were you have the control for the private key.
Yes, this is very true. You shouldn't keep any coins on the exchange unless you want to sell quickly for short profit on the same day or next couple of days. But even for day trading purpose don't keep all your money in any single exchange to avoid sudden losses if exchange goes into some trouble.
If you're buying coins for long-term gains then better move to desktop wallets and keep private keys or seeds safely so that you can access your coins in future to sell at higher price.