Understanding git rebase is important. You aren't expected to rebase mainline branches regularly but if your team operates on a merge/patchset workflow and isn't just squashing everything down onto main each PR you need to understand how to rebase your changes.

You do your development and use rebase to organise your code into logical commits/patches that can each be reviewed separately. This way when you do your review in github or on the mailing list or whatever you can review each logical change by going through and reviewing the commits separately (which you can do in github by selecting the commit in the dropdown for the review window).

And of course via email based workflows or "stacked patchset" workflows like what tangled provides then you can get deltas between revisions so that you can see what changed in a given commit between rev 1 and rev 2 so that you don't have to re-review the entire patchset/PR, only the stuff that matters (but still broken up into logical changes).

Genuine question, why? It seems like a reasonable knowledge check that can be answered in a few sentences.