The goal here is to clean up answers that do not answer the question, or are of such poor quality that they contribute nothing to the solution.
The threshold for deletion - currently 6 recommendations or 3 votes from 20K users on a post with a score <= 0 - is calculated to give ample opportunity for improvement or disagreement. Normally, anyone clicking "Looks Good" or editing will dequeue the post.
For the record: no posts on this site have yet hit the 6-recommendation threshold (a few have been deleted by 20K users). Here's an example of the sort of answer we're talking about (two recommendations, 3 20K delete votes, and a score of -1):
He is probably asking for number of decimal places?
You can certainly argue that some poor answers deserve to be left around, and you're free to act on that belief when reviewing - but for non-answers like this, there's absolutely no value in preserving them on the site; they're noise, a distraction, and a poor example for new members.
We're not trying to encourage excessive deletion here, but merely give the community at-large a say in what is deleted.