Poloniex has a serious problem with lag which can cause you to lose money on their margin trading as well as regular buying and selling.
What will happen is you'll try to close your margin position, or sell your coins, and you'll just get a spinning loading circle gif forever. Meanwhile, all your money is getting lost as the market moves.
Numerous people complain about this yet people still use Polo. I'm officially done using them after losing money for the last time.
BEWARE!
Blame the bots for causing the lag. i am pretty surprised that their servers can keep up with the traffic happening especially when most of the volumes go up.