Voting down is how the community indicates which questions and answers are least useful.
When should I vote down?Use your down-votes whenever you encounter an no-effort-expended post or an answer that is clearly incorrect.
You have a limited number of votes per day, and answer down-votes cost you a little bit of reputation on top of that, so use them wisely. Keep in mind, you should flag inappropriate and/or spam content and NOT down-vote it (why waste your reputation?)
What happens on a down-vote?When a post is down-voted, the author of the post receives a -2 in reputation. Also, the user down-voting receives a -1 in reputation if the post is an answer and no change if the post is a question.
Down-voting alternatives?If a post is spam, offensive or a duplicate, please flag it. If something is wrong, please use comments or edit the post.