They don’t.
How do I know? I got banned for arguing with a pedo apologist and telling him to go fuck himself. He replied to a comment and then blocked me so that it would seem like I was droppping off of the convo. I edited my last reply to call him out, and bam. Reddit perma-bans me for 'continuing to harass a user who had already blocked you’.
The only way to get rid of your posts and comments so that reddit doesn’t benefit from them is to delete your account.
Yup. The ban just prohibits you from engaging with communities. Like, you can’t post, comment, or upvote. You still have access to your account and feed. So, you can choose to delete it. And I think you should be able to delete individual posts/comments too, though I didn’t try that myself since I decided to just nuke my account.