PageRank and Nofollows
PageRank is a technique used for dictating the order of websites being presented in web searches. A recent article from the Search Engine Journal discusses how the nofollow attribute in HTML links prevent PageRank from accounting commented links into its calculations. The nofollow feature, which was implemented in 2005, was designed to prevent spam from influencing search results. However, Google updated how it uses nofollows in 2020. While it will not apply nofollow links into its PageRank calculations, it will use nofollow links for exploration and allow for indexing to occur.
Connecting the nofollow feature to our discussion on PageRank, we can observe why nofollow is extremely useful. So what would happen without the nofollow feature? Well, it would be easy for people/organizations to do sneaky SEO optimization. For example, if a couple links were entered into the comments and they also pointed to each other, it could basically siphon page rank from the network. This would only serve to help the spam websites and hurt the original website as well as others in the network. While there are adjustments in place so that it would not take all the PageRank from other nodes in the network, it would still negatively influence the network. The nofollow feature can help to ensure that the network is properly maintained and that search results are more accurate.
Source: Search Engine Journal