I agree completely that coins should not be left on exchanges. You see far too many pictures and videos of people showing off their portfolio of crypto where it is all on an exchange. They are risking losing it all in the event of a Mt Gox style shut down.
I appreciate it is difficult if you want to trade regularly and it can be an issue to keep track of many different wallets and back ups etc but this is by far the safest way of keeping control of your coins. Trezor now supports several coins (not sure about Ledger) but there are other multi wallets.
This advice is also particularly pertinent at the moment with the ongoing issues with Steem at Poloniex and the potential of a bitcoin chain fork, you should ensure you maintain control of your keys!