Different facilities require different options. Most deliverables today are High Definition either 720p 59.94 or 1080i 59.94. Depends on your channel or facility.
16×9 does not mean high definition however, a lot of tv stations get away with an HD look by shooting their standard definition in 16×9 so it fills the frame of an HD set, nevermind quality.
Think of Anamorphic as 16×9. You have a 16×9 wide rectangle frame, and had a circle in the middle of the screen. If you took that 16×9 footage, and played it back on a good old fasioned square 4×3 tv set, the circle would look like an egg. It would be squeezed from the sides.
The reverse is true. If you take a 4×3 square image, and stretch it to fill a 16×9 rectangle frame, your circle would turn into an oval.
So, if you are trying to make a 16×9 frame look proper in a 4×3 frame, you either have to make the frame letterboxed by adding an effect from the image-resize. Or by cropping off the extra rectangle and make it a square.
Tv stations get this wrong all of the time. When they go back to the archives, and they mix it with high definition or 16×9 footage.