In March 2006, KinderStart filed a lawsuit against Google over search engine rankings. KinderStart's website was removed from Google's index prior to the lawsuit, and the amount of traffic to the site dropped by 70%. On March 16, 2007, the United States District Court for the Northern District of California (San Jose Division) dismissed KinderStart's complaint without leave to amend, and partially granted Google's motion for Rule 11 sanctions against KinderStart's attorney, requiring him to pay part of Google's legal expenses.[70][71]
In particular, the Google web spam team is currently waging a PR war on sites that rely on unnatural links and other ‘manipulative’ tactics (and handing out severe penalties if it detects them). And that’s on top of many algorithms already designed to look for other manipulative tactics (like keyword stuffing or boilerplate spun text across pages).
Robots.txt is not an appropriate or effective way of blocking sensitive or confidential material. It only instructs well-behaved crawlers that the pages are not for them, but it does not prevent your server from delivering those pages to a browser that requests them. One reason is that search engines could still reference the URLs you block (showing just the URL, no title or snippet) if there happen to be links to those URLs somewhere on the Internet (like referrer logs). Also, non-compliant or rogue search engines that don't acknowledge the Robots Exclusion Standard could disobey the instructions of your robots.txt. Finally, a curious user could examine the directories or subdirectories in your robots.txt file and guess the URL of the content that you don't want seen.

QUOTE: “Supplementary Content contributes to a good user experience on the page, but does not directly help the page achieve its purpose. SC is created by Webmasters and is an important part of the user experience. One common type of SC is navigation links which allow users to visit other parts of the website. Note that in some cases, content behind tabs may be considered part of the SC of the page.” Google Search Quality Evaluator Guidelines 2017
Ideally, you will have unique pages, with unique page titles and unique page meta descriptions . Google does not seem to use the meta description when ranking your page for specific keyword searches if not relevant and unless you are careful if you might end up just giving spammers free original text for their site and not yours once they scrape your descriptions and put the text in main content on their site. I don’t worry about meta keywords these days as Google and Bing say they either ignore them or use them as spam signals.
A page title that is highly relevant to the page it refers to will maximise usability, search engine ranking performance and user experience ratings as Google measures these. It will probably be displayed in a web browser’s window title bar, bookmarks and in clickable search snippet links used by Google, Bing & other search engines. The title element is the “crown” of a web page with important keyword phrase featuring AT LEAST ONCE within it.
Being ‘relevant’ comes down to keywords & key phrases – in domain names, URLs, Title Elements, the number of times they are repeated in text on the page, text in image alt tags, rich markup and importantly in keyword links to the page in question. If you are relying on manipulating hidden elements on a page to do well in Google, you’ll probably trigger spam filters. If it is ‘hidden’ in on-page elements – beware relying on it too much to improve your rankings.
The ranking of your website is partly decided by on-page factors. On-page SEO factors are all those things you can influence from within your actual website. These factors include technical aspects (e.g. the quality of your code and site speed) and content-related aspects, like the structure of your website or the quality of the copy on your website. These are all crucial on-page SEO factors.