What do the PIX keys do on Sanyo 4:3 tvs?

Their website says this:
DTV Remote with PIX Shape key:
This remote control has a video input selection key to allow the user to select an A/V input source without going to the menu. Info, Audio, Caption and Pix Shape keys allow immediate access to these functions and settings.

Picture Shapes
Available options: PIX1, PIX2 and PIX3 will vary depending on the format of the signal received and aspect ratio of that broadcast format.

The manual says this:
Use to change the video display format. Available options depend on signal received and the broadcast's aspect ratio. Note: Cannot display picture on a full screen. Check Aspect Ratio of broadcast. Then press PIX SHAPE key to change setting.



I think I know what it's saying but I'm not completely sure. Does anyone know anything about this?

I've been able to determine that it allows for switching between 4:3, Stretch 4:3, and Compress 16:9.

Now, can anyone explain how and why this might be useful in a 4:3 tv? It doesn't make sense to me. Well, I get the 4:3 but what I don't understand is how the 16:9 might be useful. Aren't tv shows, movies and DVDs that display in 16:9 already displayed in a 16:9 format regardless of what kind of tv you have? I just don't get it.

Some 4:3 TVs have a compression feature so that 16:9 material like HD TV programming or anamorphic movies can make use of all 480 scan lines. If you watch something 16:9 letterboxed on a 4:3 display, then you're wasting 1/3 of the scan lines. There are also different picture modes for watching OTA, like so you can zoom in to watch a 4:3 program.

That's still a little confusing.

I tried playing around with the buttons but that didn't do a lot. When I pressed the PIX button while watching digital cable, nothing happened and I was given a message that the option was not available. When I watched a 16:9 DVD, the 4:3 option didn't seem to do anything, the 4:3 stretch option did stretch the picture but it remained in 16:9 and looked distorted. So perhaps these options are really meant for digital OTA broadcasts?