there’s information that may have been unknown to a poster at the time of writing a post that would be best included in op
there are mistakes that happen in posts which get a lot of attention that corrections made to a repost after deletion would not get, where a retraction and acknowledgement of the mistake in the op is the general ethical solution already
professional journalists with professional copy editors and proofreaders still have mistakes get through to a published story, there is no level of “make sure there are no mistakes” that will make up for the lack of edits in post
say you post something and you find yourself drowning in harassment in the comments. currently, you can ignore users, which given a critical mass becomes a futile exercise; or you can delete the op. there isn’t a way to change privacy after the fact to keep discussion going in a circle of your choosing – you can’t shut out the commenters by locking down a thread. that’s another benefit to edits.
re: implementation: version control systems provide a good example already – differences are published and merged with the prior version to make a new version and the change is logged. it’s an old problem with an old solution that works.