Ideally, we like to preserve information that has value. We let people keep reputation from votes when the content is there for several months since we like to reward half baked ideas that move the discussion forward. When a comment or an edit can preface what part is now known to be wrong - what the actual answer is (with links or just narrative), that is the best.
If there is no way to save it, you might link to it in the chat room or flag for moderator review. As long as you have the option to delete the answer, it's low enough in votes and other modifications that it remains in your power to decide to delete.
Now, nothing actually gets deleted, since high rep users, moderators and site staff see all posts - even deleted ones - there is always the chance someone will vote to reverse a deletion, make an edit, whatever.
The primary way the system suppresses bad questions and answers is by reflecting several negative votes. Once the community has expressed a net -4 vote on a post, it begins to fade away and become eligible for automatic culling without needing a moderator (elected or just a user having earned moderator tool access) to actually case a close or delete vote.
By down voting content that is not useful to you, you are starting the deletion process and helping moderate your site.
