Trading at market open/close and leaving positions open over the weekend?

Please be aware that in the minutes approaching/following the opening/closing of the market for the underlying instrument, you may experience gaps in market prices. Due to the volatility expressed during these time periods, trading at the open, at the close or leaving positions open over the weekend can involve additional risk and must be factored into any trading decision. These time periods are specifically mentioned because they are associated with the lowest levels of market liquidity and can be followed by significant movements in prices for both the spread bet and the underlying instrument.
There is a substantial risk that stop-loss orders, left to protect open positions held overnight, may be executed at levels significantly worse than their specified price.