A flight shall not be commenced unless taking into account both meteorological conditions and any delays that are expected in flight, and the aeroplane carries sufficient fuel and oil to ensure that it can safely complete the flight.
When the flight is conducted in accordance with the visual flight rules, the amount of fuel to be carried must permit:
Before departing with a light aircraft, in real flight, the pilot will fill the fuel tanks at the maximum especially if the weather is not expected to be good.
It prevents the "lack of fuel" distress during unexpected re-routing, holding or diverting to any alternate airfield.