I found this nice post and a nice decision flowchart.
Intelogy. Who can associate a site to a SharePoint Hub Low resolution, visit the post to see more.
I also have drawed a simple chart while explaining for my colleagues, you can see it above. I hope this infographics can be useful to more people. By the way, we use the word “Hubber” (sv. Hubbare) for “People who can associate sites to hubs”