Metal files are generally helpful whenever you need to remove metal, but they will also work for wood.

What's even better is a rasp. In particular, the Shinto.

Imagine a bunch of hacksaw blades stacked together in a handle. It would look like this:

This thing will reduce wood to dust in no time at all. There are two sides--one is very aggressive, the other not so much. This is probably the best wood removal tool for many reasons. Watch the video that shows this tool in action.

A metal file will be needed for many other more delicate removal operations, especially when it comes to working on frets. Those are all covered in greater detail in the re-fretting sections.