If you are in the process of trading coins, they could get stuck on the exchanges. So "never leaving them on an exchange" kind of defeats the purpose of investing. I feel that these exchanges need to be more responsible and held accountable for their mismanagement. I had BNB on Binance because it has to be there for the fee discount. I was able to trade BNB to ETH on the mobile app, and I could attempt to withdraw it, but I was stopped by the email verification because the main sight won't load. Lets face it, Binance screwed up.