Hi,
I want to earn interest on my coins (BTC,ETH,LTC) therefore I prefer to leave these in Exchange for funding purpose, however I have No plan to sell or exchange with other coin in near future.
I always keep my withdrawal blocked by changing password every 5th day.
Is it 100% safe to keep crypto's in exchange like Bitfinex or others with withdrawal locked ?
Yes but not totally you can trust the exchange fully for 100% security. If you really wanted to make your tokens/coins secure better to put it in your wallet if you don't have not yet a plan to sell it.