ACF does not delete field data when you delete a field or delete a post.
However, when deleting posts WP should be automatically deleting all post meta that is associated with that post. If it is not then there is something on your site preventing it from doing this cleanup.
The only time you should have unused data in the post meta table is if you delete a field from ACF. The data will linger until the post that it is related to is deleted.
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