Will,in my own opinion its not safe to keep some of your crypto coins in the exchanges,because of so many circumstances,and one factors of this if maybe the exchanges been hacked,or declared bankcrupt on there exchange trading,there is no guarrantee that you  can get back  all your crypto coins thats you put up on thats exchanges,so therefore its better thats you must keep all your crypto coins in your wallet,and put it only when you doing trade.