I often find myself leaving a constructive comment on a bad answer with ways to make it suited for the topics of this site rather than downvoting it because that costs me rep. Therefore, I leave it to higher-rep users to downvote bad questions and answers. For example, take this question and read the answer by Joseph Bannister Kulhavy. Rather than actually addressing the questions in the question, he simply raises more unanswered questions. I would downvote but I really don't want to lose the reputation that I worked so hard for. What should I do? I've already commented and flagged as not an answer.
In this case leaving a comment and flagging is a good solution, it will bring the question to other people's attention and it will either get deleted or down-voted or otherwise treated appropriately.
- You can down-vote questions with no cost of reputation, so if you find a bad question then down-vote freely!
- If you down-vote an answer and it later gets deleted you get your reputation back.
If you correctly flagged as Not An Answer, the reviewers will likely agree with your flag and the post will be deleted. When a post is deleted, the cost of downvoting it is refunded to you.
But suppose the post doesn't get deleted and your reputation point is lost. Then you can do your penance by suggesting a good edit to another post (this takes work, as a penance should). The balance is in your favor: one edit offsets two downvotes. If you are good at recognizing low-quality content, you should also be able to make some of the content better.