Can I only use robots.txt?

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  George G.: Not true. Robots just blocks crawling on your own site. If an outside link points to the page, it can get indexed. On the contrary noindex will always keep the page off the index.
  
  2d
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  Robbie King: George G. amazing, thank you
  
  2d
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  Jesús Moreno Casas: George G. Where I check this on Google guidelines?
  
  2d
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  Roger Montti: Jesús Moreno Casas Check Google`s Dev pages.
  
  Robots text is NOT the same as noindex and you shouldn`t use both, ever
  
  Robots = Don`t Crawl.
  
  Noindex = Don`t include in the index, including any links on the page.
  
  1d
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  Juan Dalisay Jr.: George G. How can Google index the outside link to a page blocked by robots?
  
  2d
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  Roger Montti: Juan Dalisay Jr. Google adds a robots blocked page to the index because the link tells Google it`s worth indexing.
  
  BUT the SERPs won`t show a snippet for the page.
  
  1d
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  Michael Martinez: Technically, I`m not sure there is really a justification for "noindex, nofollow" any more (at least as far as Google is concerned) because Google says once the page has fallen out of the index its links won`t be followed anyway.
  
  2d
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  Ash Nallawalla: Be careful not to combine a noindex directive with a robots.txt block, else the crawler will not get to read that noindex tag.
  
  https://developers.google.com/.../crawling/block-indexing....
  
  DEVELOPERS.GOOGLE.COMImpedir que la Búsqueda indexe páginas con la directivaImpedir que la Búsqueda indexe páginas con la directiva
  
  2d
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  Zachary Toto: There is a difference between telling search engines not to index, not to follow, and not to crawl.
  
  2d
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  Trenton Erker: Zachary Toto well that’s inaccurate. See above.
  
  2d
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  Zachary Toto: Trenton Erker Well no that`s the fact do your research.
  
  2d
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  Trenton Erker: Zachary Toto lol please see above
  
  2d