The more you use Google Classroom to assign online content the more cluttered the class STREAM can become. The TOPICS tab is an easy way to organize your assignments, announcements, and video content.
The TOPICS box is on the left side and it is very easy to add, rename, or delete a topic to suit your class needs. Every time you add an assignment, announcement, or a video there is the option to select a topic. This helps both you and your students find their work.
How about adding Google Sites to your STREAM. One issue with Classroom is there is not a good place to list daily assignments that are not posted or assigned in the STREAM. Using the TOPICS tab you can add a Google Sites web page to list classwork, homework, and a place where your students can download Google docs, PDFs, etc… I recommend you use the Move to the top option to always have the website at the top of the STREAM.