This window is a once popular way to show the focus of the content on the website. The most used tags are larger than the less ones. You can click on a tag to get to the search results page narrowed down by a chosen tag.
Remember that Calendar module records are very short. If you want a longer version of an event description you can always attach an article to a specific event. It can be a news article from your news feed or just a special article you wrote to make a story about what is gonna happen.