When you turn the spark wheel of flint lighters, the spark wheel turns against a little stone called flint. The friction between the spark wheel and flint generates spark. When butane gas meets this spark, flame is ignited. If you open the cap of flint lighters, butane gas from the gas tank of flint lighter is automatically released. After you use flint lighters, you need to close the cap in order to extinguish the flame and also, to prevent butane gas from evaporating. Some smokers prefer flint lighters because:
1) the flame is visible
2) once the flame is ignited, the flame will stay on even though you do not continuously hold down the ignition button or wheel of the lighter.