I'm trying to figure out the right strategy to differentiate between content I want to appear in search results, and content I don't. I've found example in which a site has unique content, which has ranking value, and he chooses to not put it in search results.
An example is MOZ open site explorer, which is a free seo analysis of a website. Their page about stackoverflow could be a good target for seo, but they chose not to allow it (through robots.txt). This is the page itself: https://moz.com/researchtools/ose/links?site=stackoverflow.com&filter=&source=external&target=page&group=0&page=1&sort=page_authority&anchor_id=&anchor_type=&anchor_text=&from_site=
What are good reasons to make such a decision from an SEO perspective? If you add a page, does that mean other pages will potentially lose ranking?