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? ..
QUOTE:  Each piece of duplication in your on-page SEO strategy is ***at best*** wasted opportunity. Worse yet, if you are aggressive with aligning your on page heading, your page title, and your internal + external link anchor text the page becomes more likely to get filtered out of the search results (which is quite common in some aggressive spaces). Aaron Wall, 2009
When Googlebot crawls a page, it should see the page the same way an average user does15. For optimal rendering and indexing, always allow Googlebot access to the JavaScript, CSS, and image files used by your website. If your site's robots.txt file disallows crawling of these assets, it directly harms how well our algorithms render and index your content. This can result in suboptimal rankings.

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When would this be useful? If your site has a blog with public commenting turned on, links within those comments could pass your reputation to pages that you may not be comfortable vouching for. Blog comment areas on pages are highly susceptible to comment spam. Nofollowing these user-added links ensures that you're not giving your page's hard-earned reputation to a spammy site.
In the enterprise space, one major trend we're seeing lately is data import across the big players. Much of SEO involves working with the data Google gives you and then filling in all of the gaps. Google Search Console (formerly, Webmaster Tools) only gives you a 90-day window of data, so enterprise vendors, such as Conductor and Screaming Frog, are continually adding and importing data sources from other crawling databases (like DeepCrawl's). They're combining that with Google Search Console data for more accurate, ongoing Search Engine Results Page (SERP) monitoring and position tracking on specific keywords. SEMrush and Searchmetrics (in its enterprise Suite packages) offer this level of enterprise SERP monitoring as well, which can give your business a higher-level view of how you're doing against competitors.
This broken-link checker makes it easy for a publisher or editor to make corrections before a page is live. Think about a site like Wikipedia, for example. The Wikipedia page for the term "marketing" contains a whopping 711 links. Not only was Check My Links able to detect this number in a matter of seconds, but it also found (and highlighted) seven broken links.
After the audit has been completed, your team will be invited to a presentation in which your SEO specialist will talk through the findings and recommendations. The Three Deep SEO team will walk you and your team though the roadmap to completion so you know what to expect and when. In addition, you will receive a comprehensive analysis of your site’s health. All of these are customized to you and your specific situation.