Many blogs, including this one, generate duplicate content. For example, the archive pages duplicate the content of individual posts, they just show them in a different way (a couple of posts per page, as opposed to a single post per page).
That unfortunately clogs search engines. Being a perfectionist that I am, I want that a search for e.g. “15minutes” (my simple timer application) leads people to individual blog posts about it and not to aggregate pages with random other content.
User-agent: * Disallow: /page/ Disallow: /tag/ Disallow: /notes/
In my particular case, archive pages all start with
/tag/ is another namespace with duplicate content (shows a list of articles with a given tag).
For this technique to work the names duplicate pages have to follow a pattern, but that’s easy enough to ensure, especially if you write your own blog software, like I do.