QUOTE: “Expertise, Authoritativeness, Trustworthiness: This is an important quality characteristic. …. Remember that the first step of PQ rating is to understand the true purpose of the page. Websites or pages without some sort of beneficial purpose, including pages that are created with no attempt to help users, or pages that potentially spread hate, cause harm, or misinform or deceive users, should receive the Lowest rating. For all other pages that have a beneficial purpose, the amount of expertise, authoritativeness, and trustworthiness (E-A-T) is very important..” Google Search Quality Evaluator Guidelines 2019
Many think that Google won’t allow new websites to rank well for competitive terms until the web address “ages” and acquires “trust” in Google – I think this depends on the quality of the incoming links. Sometimes your site will rank high for a while then disappears for months. A “honeymoon period” to give you a taste of Google traffic, perhaps, or a period to better gauge your website quality from an actual user perspective.
It makes sense, even in 2020 that this process of labeling is how you create a Search Engine Results Page out of pages Pagerank 2020 identifies, identify spam, identify monetisation trends and promote content first pages and user friendly content above others. You can also imagine that over time, Google should get a lot better at working out quality SERPs for its users, as it identifies more and more NEGATIVE ranking signals, thereby floating higher quality pages to the top as a second order effect. A end-result of this could be that Google gets an amazing SERP for its users.

QUOTE: “Anytime you do a bigger change on your website if you redirect a lot of URLs or if you go from one domain to another or if you change your site’s structure then all of that does take time for things to settle down so we can follow that pretty quickly we can definitely forward the signals there but that doesn’t mean that’ll happen from one day to next” John Mueller, Google 2016

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.

And you’ve got to diversify. Here’s a tongue-twister that’s absolutely true: diversity is a key word in the keyword world. You’re not going to stand out if you find yourself using all of the same keywords as your competitors. Not only should you try new keyword search tools and keep track of the results, but you should feel free to experiment based on your own research – who else uses your keywords? And how do you make yourself stand out? By providing great content that truly answers the questions your prospective customers are asking with their keyword searches.
Ask for a technical and search audit for your site to learn what they think needs to be done, why, and what the expected outcome should be. You'll probably have to pay for this. You will probably have to give them read-only access to your site on Search Console. (At this stage, don't grant them write access.) Your prospective SEO should be able to give you realistic estimates of improvement, and an estimate of the work involved. If they guarantee you that their changes will give you first place in search results, find someone else.