This plugin is deprecated and no longer in active development. The functionality has been included into the maven shade plugin. Please use that instead. See http://maven.apache.org/plugins/maven-shade-plugin/
This plugin analysis the (transitive) dependencies of a project on the class level. Quite often you don't need all that classes from dependencies like commons-lang (just to give an example). Maybe you use 1-2 classes. So what to do? Copy-and-past the code you need? Don't! Minijar can create a mini version of your dependencies that just fulfills your needs.