If you ever need to temporarily override the directory Maven uses for your local repository when running Maven from the command line, you can do so by setting the property
$ mvn -Dmaven.repo.local=/tmp/repository install
Why would you want to do this? I found a useful situation while logged into a server at work where my login had a form of "read-only" access, and therefore no home directory, but where I had access to Maven and needed to test something out. I'm sure there would be other reasons out there as well or the property wouldn't be available?