The essence of custody on exchanges is: whoever holds the private key holds the coins. Storing on an exchange = voluntarily giving up your private key in exchange for matching convenience and liquidity. So, this isn’t a binary issue of 'safe or not,' but rather a pricing question of 'how much counterparty risk are you taking on for how much convenience.' Boundary condition: If you’re doing high-frequency trading and need instant in-and-out access, keeping a certain balance on the exchange is unavoidable. The underlying logic doesn’t reject a turnover wallet, it only rejects leaving your base holdings on the exchange.