...
Single commit should always represent a single, completed chunk of work. We should avoid mixing in unrelated stuff - eg. combining two tickets together or adding in a major refactor. Having some changes in one class that has also undergone a major refactor makes it hard to review and determine which parts were added/modified and which were only refactored. Squashing commits together well can help the reviews stay focused and clear. As you choose which commits to squash together, the idea is to squash for atomicity, cleanliness and to make the code history readable during review.
...