It is not good to keep all coins in a single exchange. Because if it is shutdown all coins will be lost.
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.
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.
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.