Previously, it was impossible to continue reading posts on similar topics as the one you just read. If you were starting on the main page and wanted to find a post on some specific topic, the only option was to go by the title, which doesn't always tell the full story.
Starting today, all posts are connected to one or more related topics. On the main page, you can easily select and search for topics you're interested in, and on posts, you can select a topic you want to continue reading about.
This change has made it incredibly easy to find content on a specific topic, something I need frequently.