I took the tour and looked around the site, but couldn't find an answer to this. What is the protocol for down-voting an answer on Puzzling just because it is not the correct answer? I would assume it is not encouraged since puzzles by definition are meant to be tricky, and meant to elude a correct answer.
While I don't DV for answers being wrong (-and I don't think I've DV (m)any answers at all-), I would DV an answer which gives reasoning against logic (or the logic of the puzzle.), i.e. if there is a riddle, and I's see an answer giving 'explanations' to each clue which are just totally out of the blue etc.
In other words, being just wrong is not a reason for DV, but bad quality answer can mean more than just "missing text". A very long and detailed answer can still be of very bad quality, although I have not yet come across any.
Another example would be an answer which clearly ignores instructions from the puzzle. i.e. if the puzzle askes for a mathematical solution in an image, and the answer just is of type ...if I look at it, I could imagine seeing..., then this would get a DV from me.
I'm assuming this is in line with the recent surge of downvotes without any reasoning on several questions asked recently. (The note of anger you may detect is because I got downvoted myself and it really pisses me off when it isn't warranted)
I guess: You should downvote if an answer is not explained, or off topic (not an answer to the question asked). You should always explain in the comments WHY you downvoted, unless it already has been explained by someone else. Most common downvotes are normally as A E said, a lack of explanation often on incoherent answers. Occasionnaly you'll get somewhat 'stupid' answers meant to be humoristic etc.. those can be downvoted - people who post em normally know to expect them. Allthough I wouldnt (downvote). It's all supposed to be in good fun isn't it?
Let's not turn SE into youtube debates. (if you are downvoting based on your personal opinions, it's for the wrong reasons)
EDIT: as an additional note,
Puzzling differs from some of the other SE sites (notably Stack Overflow) in that a wrong answer doesn't really lead to any consequences. Wrong answers are common on Puzzling because of the nature of the questions asked, and we encourage (most of the time) attempts to answer.
On Stack Overflow, wrong answers can mislead people and basically waste time - they are downvoted to discourage people from talking out of their hats and leading people astray.