If you delete a blog you will not be able to get it back and no one else will be able to use that blog address. You must be sure you never want to use the blog again if you delete it. If you are unsure, you can change the blog to private and no one will be able to read it. If you decide to use it later, you can switch it back to a public blog.
Do NOT delete a blog to transfer it to someone else.
Do NOT delete a blog to create a new username.
Do NOT delete a blog to get rid of old posts or other content.