Commit history (preferably of a non-pushed path, since it rewrites hashes) can be edited; useful for feature branches with useless commits / debug messages / strange orders and so on -- things which happen during committing, but should not stay in the end-product.

• best article: https://git-scm.com/book/en/v2/Git-Tools-Rewriting-History
• why squash?: https://jamescooke.info/git-to-squash-or-not-to-squash.html
• rebasing basics: https://git-scm.com/book/en/v2/Git-Branching-Rebasing
• some workflow recommendations: http://justinhileman.info/article/changing-history/
• additional tips (mostly covered in first link tho): https://www.maykinmedia.nl/blog/2017/nov/20/git-rebasing-make-your-commit-history-pretty/