Many blogging software packages automatically nofollow user comments, but those that don't can most likely be manually edited to do this. This advice also goes for other areas of your site that may involve user-generated content, such as guest books, forums, shout-boards, referrer listings, etc. If you're willing to vouch for links added by third parties (for example, if a commenter is trusted on your site), then there's no need to use nofollow on links; however, linking to sites that Google considers spammy can affect the reputation of your own site. The Webmaster Help Center has more tips on avoiding comment spam40, for example by using CAPTCHAs and turning on comment moderation.
Page and Brin founded Google in 1998.[23] Google attracted a loyal following among the growing number of Internet users, who liked its simple design.[24] Off-page factors (such as PageRank and hyperlink analysis) were considered as well as on-page factors (such as keyword frequency, meta tags, headings, links and site structure) to enable Google to avoid the kind of manipulation seen in search engines that only considered on-page factors for their rankings. Although PageRank was more difficult to game, webmasters had already developed link building tools and schemes to influence the Inktomi search engine, and these methods proved similarly applicable to gaming PageRank. Many sites focused on exchanging, buying, and selling links, often on a massive scale. Some of these schemes, or link farms, involved the creation of thousands of sites for the sole purpose of link spamming.[25]
Online readers don’t read – they scan. Just like you are probably doing right now. So you should write short sentences, add subheadings and use connecting words. Do you think that’s a lot harder than it sounds? 

No worries. Yoast SEO will tell you exactly what to do, based on scientific research on readability, such as the Flesch Reading Ease score.

QUOTE – “So it’s not that our systems will look at your site and say oh this was submitted by a user therefore the site owner has like no no control over what’s happening here but rather we look at it and say well this is your website this is what you want to have indexed you kind of stand for the content that you’re providing there so if you’re providing like low quality user-generated content for indexing then we’ll think well this website is about low quality content and spelling errors don’t necessarily mean that it’s low quality but obviously like it can go in all kinds of weird directions with user-generated content…” John Mueller, Google 2019
The errors in technical SEO are often not obvious, and therefore one of the most popular. Mistakes in robots.txt and 404 pages, pagination and canonical URLs, hreflang tags and 301 redirects, http vs https and www vs non www versions: each of them can seriously spoil all efforts to promote the site. One quality SEO website analysis is enough to solve all the main problems in this part forever.

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.
Having a ‘keyword rich’ domain name may lead to closer scrutiny from Google. According to Moz, Google has “de-prioritized sites with keyword-rich domains that aren’t otherwise high-quality. Having a keyword in your domain can still be beneficial, but it can also lead to closer scrutiny and a possible negative ranking effect from search engines—so tread carefully.”
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.

QUOTE: “If an off-domain link is made by an anonymous or unauthenticated user, I’d use nofollow on that link. Once a user has done a certain number of posts/edits, or has been around for long enough to build up trust, then those nofollows could be removed and the links could be trusted. Anytime you have a user that you’d trust, there’s no need to use nofollow links.” Matt Cutts, Google 2006
You can confer some of your site's reputation to another site when your site links to it. Sometimes users can take advantage of this by adding links to their own site in your comment sections or message boards. Or sometimes you might mention a site in a negative way and don't want to confer any of your reputation upon it. For example, imagine that you're writing a blog post on the topic of comment spamming and you want to call out a site that recently comment spammed your blog. You want to warn others of the site, so you include the link to it in your content; however, you certainly don't want to give the site some of your reputation from your link. This would be a good time to use nofollow.
Your website is the “hub” of your online brand – so, it’s important to have regular checkups to ensure everything is in order. It’s also important to note that your website is a living digital property, it’s typically not stagnant for long periods of time. In any given year, content is added and/or removed from your site. It is for this reason that audits should occur on a regular basis. We recommend that websites be audited at a minimum of once per year. That allows your teams to fix critical issues as they arise.