The magnesium is just a little extra bonus to help make the transition from ferro rod spark to flaming tinder.

Ferinstance, if you have nice tinder like a cotton ball or some well prepared cedar bark you don't need the magnesium. However, if your bark is a bit damp and doesn't quite catch the spark, a few flakes of magnesium can help.

Forget about making a pile of shavings - its a lot of work and a frustrating waste of time. Just make your usual tinder "nest" with a thumb sized hollow. Scrape some Mg into the hole and hit it with a spark.