Trend lines are drawn on charts to help predict the general direction of price.It also help to determine good entry and exit point.they also help to see the reversals.
It is definitely a myth that Forex traders have to observe the market and sit before your PC 24 hrs. No one can do that ! This story spread because Forex works from Sunday to Friday but it is not needed. Traders can close the trade at a specific position. They can even 'Stop loss orders' when market reaches a certain level. So no need to lose your precious sleep over trading. Forex has tremendous value for the sleep of its traders