I think that it is important to realise that every market has times where the liquidity is high and times when it is low. This can easily be seen by looking at a chart showing the trading volumes during the day:
Img 1.1 – Trading Volume changes throughout the day. Every market tends to have time periods where the volume is high, and periods where the volume is low.
An Economic Calendar will show news events or data releases related to the Economy. Each data release tends to be graded into Low, Medium and High impact events, with High Impact events commonly being marked red:
Img 1.2 – Economic Calendar. High Risk events are market in Red, Medium Risk in yellow and Low Risk in Grey.
The events market in Red are of particular importance because they can be associated with high levels of volatility. I believe that because many traders know that these events can be extremely volatile, they close out any pending orders and avoid taking on any new trades until after the data has been released.
Because it may not be possible to trade over the weekend and because there is always a risk of an important event coming out over the weekend, I prefer to shut down any open positions before the Weekend unless I am considering a trade in a high time frame.