The Netting system allows only one position open in any direction for one instrument. The system is used all over the stock market. To put it simpler, the trader cannot open selling and buying position on one instrument simultaneously - the positions mutually close, the orders open in one direction summing up.
Hedging risks is an essential ability for both new and advanced investors. Risk hedging is used when a trading system no longer works, and you've got to secure your capital against the volatile market conditions.