My own understanding keeping of Tokens on Exchange are not adequate because exchange can get hack at any time, and to avoid story that touch the heart is better to save our coins in a personal wallet. Is good to keep our Token in our personal wallet so we can control every thing in it, I know exchange has high security but is not still save. And their are very high rate of scammers if eventually the exchange got hack and they decided not to pay you won't hole any body so to avoid Lost of funds and coins it better to keep your coins in Your personal wallet.