The transparency you provide on your website in text and links about who you are, what you do, and how you’re rated on the web or as a business is one way that Google could use (algorithmically and manually) to ‘rate’ your website. Note that Google has a HUGE army of quality raters and at some point they will be on your site if you get a lot of traffic from Google.
You may not want certain pages of your site crawled because they might not be useful to users if found in a search engine's search results. If you do want to prevent search engines from crawling your pages, Google Search Console has a friendly robots.txt generator to help you create this file. Note that if your site uses subdomains and you wish to have certain pages not crawled on a particular subdomain, you'll have to create a separate robots.txt file for that subdomain. For more information on robots.txt, we suggest this Webmaster Help Center guide on using robots.txt files13.
QUOTE: “So sites that don’t have much content “above-the-fold” can be affected by this change. If you click on a website and the part of the website you see first either doesn’t have a lot of visible content above-the-fold or dedicates a large fraction of the site’s initial screen real estate to ads, that’s not a very good user experience.” Google 2012
However, if possible, I would like you to expand a bit on your “zombie pages” tip..we run a site where are definitely enough pages to delete (no sessions, no links, probably not even relevant with the main theme of the site, not even important for the architecture of the site)..Nonetheless, I am not very sure what is the best technical decision for these pages…just deleting them from my CMS, redirecting (if there is a relevant alternative) or something else? Unindex them on Search console? what response code they should have? ..