There's only one rule: anything in the master branch is always deployable

Commits create a transparent history of your work that others can follow to understand what you've done and why

Pull Requests initiate discussion about your commits. Anyone can see exactly what changes would be merged if they accept your request

Once a Pull Request has been opened, the person or team reviewing your changes may have questions or comments

Once merged, Pull Requests preserve a record of the historical changes to your code