What are the "good" reasons for deleting someone else's answer? And, related, — can you delete someone's answer with no reason? — how many delete votes does it take to delete an answer?
It depends on who you are as to how many votes are required.
Users with less than 10K reps can delete their own content, with the exception of questions that have upvoted answers attached to them.
Users with 10K+ reps can cast delete votes on other people's content, and it takes three votes to delete something.
Moderators can delete with only one vote, so not exactly a vote.
Reasons to delete something are that:
- it's spam — An unsolicited advert, but this should be done by flagging rather than delete votes. 6 spam flags delete a post, and help inform the system what spam is.
- it is other nonsense — This covers two main types of problem. First of all there is gibberish, e.g. "a;dsfh;hulasdfs". Secondly there are offensive posts. It could be argued that both are offensive.
- it does not attempt to answer the question at hand — This doesn't include wrong answers, but does include questions and comments (either on the question or one of the answers) posted in the "Your Answer" box.
- it is very low quality — This is more subjective in definition. Answers that don't explain their rationale are typically what I would call low quality. Especially single word request answers that amount to no more than "you can use <this word> for that." I would also include answers that are posted after another answer with (almost) the same answer but are less informative. Low quality answers don't always have to be deleted, if a downvote and/or comment give enough incentive for the answer to be improved then the answer can stay.