NewInstance

Local repository modules are useful when your project depends on some jars that cannot be found in any public or proprietary repository. In such cases, you have two choices: importing the jar in your local repository manually before running the build, as suggested in the mvn faq, or make your build process do it for you automatically; this is how: A Maven-friendly Pattern for Storing Dependencies in Version Control.
I learned this "pattern" time ago working with Greg in a company that was not using maven, so didn't had any repository for proprietary libraries. The solution was working great automating the process of installing the proprietary jars into the local repositories, and was saving developers to execute many maven esoteric command lines to import jars one by one.

To deploy files in a local repository module, it's possible to use the goal "deploy:deploy-file" as indicated in the example here:

mvn deploy:deploy-file -Durl=file://C:\m2-repo \
                       -Dfile=your-artifact-1.0.jar \
                       -DgroupId=org.some.group \
                       -DartifactId=your-artifact \
                       -Dversion=1.0 \
                       -Dpackaging=jar \
                       -DgeneratePom=true 

I promised to myself to write an howto about this interesting topic, as it may be useful to myself in future and I need an online reference to this procedure. But recently I don't have much time to blog, so I have to reference an existing article.

Another reference: a feature request opened by Greg to Maven team MNG-3989.