With me being a relative newbie to Super User, I am trying to understand how the system works.

As per the SU FAQ, questions have to meet certain standards, and that low quality ones will be closed. I understand that we need these standards in order for Super User to be a high quality Q&A site.

What I want to know:

• How does closing ensure higher quality posts? Closed off-topic questions, for example, only clutter up search. Why don't we delete these instead of closing them?
• And when is is appropriate to delete a question?