In the past, gas powered appliances relied on a pilot light to ignite the gas. A pilot light is a small flame that burns from a gas supply that is constantly flowing. This means that you are wasting gas, and it does present a potential safety hazard. With gas flowing all day long, it will add up to a significant amount over the stretch of a year. If the flame were to go out on your pilot light, you could potentially have gas leaking out and collecting. There should be an emergency shutoff valve for when the pilot light goes out, but this doesn’t mean that they never malfunction.
Before reigniting an extinguished pilot light you should make sure that the area is ventilated well and that you can’t pick up the smell of rotten eggs which would indicate the presence of gas. If you do have an appliance with a pilot light, it would definitely be worth considering an upgrade. A modern appliance will usually be safer, as well as, more efficient.