Coins should always be considered in a safe storage, there are lot of wallets and platform that could be used to hold coins, both of this has good side and bad. Where will you choose to store or hold your coins, in a close source wallet (exchanges) or an open source wallet like electrum and Hodler wallet?
I prefer to save or hold exchangers, because that's easier and doesn't use many transactions in transferring funds, especially so far my funds are still safe from loss(hacking). Other than that, if we store in exchangers we will not miss the moment of flash pump or dump.
As long that exchanger really trusted and we already sure to save money in that place, i think it is not wrong. Even a lot of people said that if we save money in exchanger, we not control our money, we don't have any choice especially traders who trade anwhere and anytime.