Honestly, even if may not be that popular a topic, I say go ahead and just create it now anyways. Sure, maybe you are the only one that will comment or post in a thread on "Eight Days That Made Rome" but I say go ahead and create a specific thread for that show anyways if you want to comment on it. Maybe someone else will add to it later or just want to see your specific comments on that show. Making the topic will make it easier to find those comments.
If I want to find comments on Arrow or Breaking Bad right now, for example, I have to go through pages and pages of posts in the Rate the Last TV Show thread spanning many years as new seasons and episodes aired. In between there will be all kinds of posts about other shows. Now, those comments will hopefully be easier to find and better grouped together moving forward.
At the same time, I don't want to see someone just coming in and creating a topic for every single movie and TV title they can think of just to up their post and thread count. If you do feel like commenting on something or trying to start a discussion on a title or series that doesn't have a thread yet then feel free to start on at that time and not because you want to have another thread to your name with no intention of participating on the topic.