Commitizen for contributors
When you commit with Commitizen, you'll be prompted to fill out any required commit fields at commit time. No more waiting until later for a git commit hook to run and reject your commit (though that can still be helpful). No more digging through CONTRIBUTING.md to find what the preferred format is. Get instant feedback on your commit message formatting and be prompted for required fields.
Commitizen for project maintainers
As a project maintainer, making your repo Commitizen friendly allows you to select pre-existing commit message conventions or to create your own custom commit message convention. When a contributor to your repo uses Commitizen, they will be prompted for the correct fields at commit time.