See my comment reply to Chris2048 below your comment.

It's a wiki like system that helps you to create a second brain of sorts. You write down what you do, and link between lots of different pages, such as "aws" to "ec2" to "vm" to "vmware" to "vmotion". Roam (and org-roam, an Emacs module that I use) shows you what links back to a page, which is incredibly helpful for remembering knowledge and how things fit together.

Seems to me this is like tagging, but instead of making the tags at the end of your thought, you're annotating words within your writing, which become the tags. I grant you that it is more intuitive to do it this way.