Most movies are shot with an aspect ration of 2.35:1. Some were shot 1.85:1. A 16x9 TV screen is about 1.78:1. An old 4x3 TV is 1.33:1.
There seems to be a misconception that because a letterboxed movie has black bars on top and bottom, it has lost something. It hasn't. It is simply being sized so that a 2.35:1 frame can be viewed on a 1.78:1 or 1.33:1 screen. Nothing is lost.
If the movie isn't letterboxed, you are loosing a big chunk of the frame from the sides. If you don't mind missing part of the movie, well Ok.
Going back to when DVDs first were made, there were anamorphic (package usually said 'enhanced for widescreen TVs) vs non-anamorphic (sometimes called letterboxed).
Non-anamorphic means the frames are formatted as a 4x3 picture with black bars included as part of the picture data. It displays correctly on a 4x3 TV, but on a 16 x 9 TV it displays as a small 4x3 frame in the center of the screen, and you have to zoom it to fill the screen. This also lowers the picture quality - picture data is wasted on the black bars.
Anamorphic movies are encoded so ALL of the data is picture data. On a 4x3 TV, it appears compressed - everyone is very narrow. It displays normally on a 16x9 screen.
I doubt anyone makes non-anamorphic movies DVDs today.