iston eases your vendor branch management worries. A vendor branch is when you copy a vendor's code (plugins, gems, etc) inside your own repository / project.
What are the advantages of doing that?
* You don't depend on another repository to deploy to your staging or production machines;
* You are insulated from upstream changes, until you really want those changes and have a chance to test them;
* Piston allows you to apply local patches to your vendor code, until the upstream maintainers have applied them.