Some content is wider than 16:9 and some is narrower so depending on what you are watching you will get black bars at the top and bottom or on the sides of the picture. The only way to fill the screen is to crop the tops or edges of the content. If you are watching modern (post 2005 or so) TV content that will usually be exactly 16:9.
Ok I have read the forums as well as others and I keep getting conflicting answers. I just bought a 60" sharp and I'm wanting to get rid of the Black horizontal bars at the top and bottom of the picture.