Non-Square Pixel Rendering - Ulead Videostudio 8

Just started using Ulead Videostudio 8. One of the options when rendering
video to a file is "Perform Non-Square Pixel Rendering". Because it was a
default I went with it.

After rendering about 4 tapes of DV AVI video to MPEG2 using this option, I
finally noticed a strange thing - the resulting rendered video appears to
have 720x480 frames, but the actual image occupies only 640x480 of this
720x480 frame. In each frame, there is a 40-pixel black bar on either side
of the 640x480 video image.

I can't see any use in doing this. Wouldn't I be stuck with the 40-pixel
black borders, for example, if I burned the file to a DVD for playback on a
standalone player?

I'm thinking it's better to render the video as a 720x480 image. Sure, a
720x480 image is stretched width-wise when viewed on a computer monitor
(with its square pixels), but when viewed played back on a TV with its
skinny pixels, it appears in proper 4:3 aspect ratio.

Also, don't most computer video players automatically display the video in
the proper aspect ratio? For example, when I play back a 720x480 video file
(rendered with the "Perform Non-Square Pixel Rendering" option turned off),
Windows Media Player displays it with a video size of 720x540 - 4:3 ratio.

Am I misunderstanding this? Can anybody explain why I'd want to turn this
"Perform Non-Square Pixel Rendering" on?