I am bittrex user.and we can place order for a sell price and when that price reaches, coins are automaticaly sold.So if its same with the poloneix or cryptopia then automatic selling can be beneficial for you..but some times you put up a buy price and what happens is that coin price rises but does not rise that much that your coins automatic sells.so when person sees this then it breaks your heart.sometimes price rises much above your fixed value and your coins are sold at your fixed price but when you see that price is much high you just feel heartbroken again. but autmated selling can give you profit obviously if you keep emotions out of it.