Use Amend When
You just made the last commit and want to fix a message or include a forgotten file.
The commit has not been shared yet and rewriting it will not surprise anyone else.
Compare
git commit --amend vs new commit
When to revise the last commit and when to add another commit instead.
Amend rewrites the most recent commit. A new commit preserves the previous one and adds another step to history. The main question is whether history rewriting is still safe.
Use a New Commit When
The original commit is already pushed or part of shared history.
You want an explicit follow-up change rather than hiding the correction inside the previous commit.
Rule of Thumb
Amend before sharing. Add a new commit after sharing.
Want the short version? Browse the compact sheet views and save the commands you use most into a Cheatbook.