/privileges/trusted-user does not explain how to best apply the delete answers privilege.
Here's a little comparison. First, I quote access to moderator tools privileges explanation for deleting questions (it says Deleting posts in the title, but that's apparently not precise):
When should I delete questions?
Closed questions that are of no lasting value whatsoever should be flagged and deleted.
Before voting to delete, please check that there are no good answers — if so, then the question should be flagged for moderator attention as a potential merge candidate. We don't like to lose great answers!
Also, be cautious when deleting questions closed as duplicates — they can serve as a signpost, directing users to useful answers on another question.
It takes 3 votes, minimum, to delete a closed question. However, the number of delete votes required scales to the number of votes on the question and all its answers.
You must wait for a question to be closed for 2 days before you can vote for deletion. This restriction is removed for trusted users. If you feel a post should be deleted despite having lots of votes or for being new, please flag it for community moderator attention.
You can view a list of posts with outstanding delete votes via the moderator tools delete tab.
Here's the explanation in the trusted user privileges page:
What are trusted users?
Trusted users are allowed to perform trusted actions, including:
Voting to delete answers with score of -1 or lower
That's really all there is about this. The rest of the page goes on about what tag wikis are. If you managed to get 20k+ reputation and don't know what they are, you're probably doing it wrong.
But it says absolutely nothing about when it is appropriate to delete answers.
As a long-time user, I am familiar with closing questions, and that's an indicator a question isn't good. With the additional explanation on the question deletion privilege, I have an idea how to act.
But deleting answers? I have no idea what answers need to be deleted. Except maybe those I flag as spam or offensive, but is this all we should use this for?
This is a bug report against the user documentation.