I don't see why why I should be warned about being made unable to ask or answer for deleting questions and answers I've put up when they have been deemed off-topic and closed, or voted down and become "protected" by Stack Exchange moderators.
When you delete a question or an answer they contribute to a Q&A which can become more valuable than either in isolation. These Q&As have contributions from others in the forms of comments, edits and votes, further increasing their potential value to the site.
As just one contributor to a Q&A, I think it quite reasonable that you are discouraged from viewing the deletion of a chunk of it as something that only impacts you. Doing that can leave the remainder gutted which is why only higher rep users and moderators can vote for their deletion.
You can delete some of your own posts but my advice would be, as per the warning, to think about whether you really want to.