Chinese bitcoin exchange Huobi just took 46% of its BTC futures traders (margin traders) profits from the past week in order to cover a loss of 1 million dollars that it suffered when a customer went bankrupt trading bitcoin at 20x leverage during the huge rise last week, and then it couldn't exit the trade.
First off, 20x leverage in bitcoin is utter insanity. This market is nowhere near liquid enough, and the moves are too large, for 20x leverage to work. This is shown by the fact that Huobi managed to lose 1 million dollars because it allowed its traders to use 20x leverage. At that amount of leverage, in a market as small as bitcoin, there is no way to unwind the losing trade properly once you give the margin call to the trader. Apparently this margin call took the price all the way down to 2378 CNY, after being issued at 2817! If you want to know why bitcoin went up to 2900 last week and then crashed back down, this is why!)
But this event points out the benefit that Bitshares has over a trusted 3rd party exchange.
With Bitshares, you make trades on the blockchain. If you short bitUSD (essentially taking a margin long position in BTS), the result is going to be enforced in the blockchain.
If you make profits, they are your profits, and no one can take them from you without your private key.
Because you are using a decentralized system, rather than trading in a central exchange, there is no one who can do what Huobi just did, and steal your profits.