There are many benefits to getting your trademark federally Registered with the United States Patent & Trademark Office (USPTO). Here are a few:
You can only legally use an R in a circle symbol when you have a federally Registered Trademark. That means the United States Patent & Trademark Office has issued you a Registration Certificate for the exact Mark you are using. You cannot use the R in a circle symbol while your trademark application is pending or before you file the application. However, you may use the SM (service mark) or TM (trademark) symbols at any time.
You cannot copyright a title or a short phrase. Also, you cannot register a title to a single book, tv show, movie, etc. as a trademark. However, you can federally register a title of a series of books, movies, tv shows etc. as a trademark. For example, Harry Potter is a series of books and "Harry Potter" is a federally Registered Trademark. To have a "series", you need to have more than one.