I really don´t get it - how can anyone leave bigger amount of coins on exchange, which (honestly) look like middle school project? The game is rough, hacks and scams happens over and over again all the time and if You don´t want to loose Your coins, send them somewhere, where You can expect at least some security. If You don´t care about security, let it go. THIS IS NOT A BANK, NOR FOREX!
As a miner I agree that you should not keep your money at any exchange, gotta withdraw em as fast as possible
But if some1 is an exchange gambler who buys/sells coins all day his coins balances are his tools. He can't withdraw his whole balance, coz if he would there will be nothing to gamble with. I beleave these exchange gamblers are in fact main buyers of coins that we mine. If not for them mining would not be profitable coz coins don't cost shit without a gambling opportunity.