Versioning is more than just slapping an incremental number on your new release. A good version increase will let the users of your package know more than just a new release. Most of us will understand the difference between major and minor versions. However, using a proper versioning scheme can help people a lot with what the impact of the upgrade will be.
This post will try to give some context to the Symfony versions. What to be aware of with a new release, be it a patch, minor or major version bump.