it's just backup of current state with irrelevant commit message. Everything is described at the end of the work in PR's description and squash merged.
Unfortunately a good chunk of the industry doesn't have the discipline to do this.
If you have ever worked in a project where there was discipline around committing, you know there is lots of value in doing so (rebasing becomes easier, you unlock the power of bisect, log is actually useful).
Also doing PR code review is soo much nicer if each commit is logically self contained with a nice commit message.