No fire kit is complete without one. Even if you carry a lighter.
Now, it's no secret that Flint and Steel is my favorite method for starting fire. And although flint and steel, bow drill, fire piston, solar ignition, etc. are more fun*, they all have their downfalls.
First, they are primitive. They require a certain degree of skill. They require manual dexterity, and a little bit of luck! Additionally they need meticulously prepared tinder bundles. These methods are extremely vulnerable to moisture in the materials. Even if the moisture is just in the air, it can give you fits. When the charred materials or friction fire components get wet, you are going to have a devil of a time getting things to ignite.
The only thing necessary for fire by firesteel, is a marginally dry tinder source. Fatwood shavings and birch bark are extremely reliable tinders with this method. Dryer lint, petroleum jelly infused cotton balls , and pine needles are also effective tinders. Using a firesteel is going to give you a better chance, every time, to achieve fire. Even when soaking wet.
In this video we'll run through a couple of different firesteels and a handful of the materials that can be used to affect fire....
*in my biased opinion