On the source material, yes. But display devices may introduce some delay on the video due to scaling, de-interlacing, temporal noise reduction, and whatever other processing is done. The display device then needs to signal back to the amp how much delay it's introducing into the video so that the audio can be delayed by the same amount.

If you connect your source through an surround processor it helps to be able to delay the audio to match the delay of the TV which may vary depending on TV settings (e.g. Game mode may be lower delay but with less picture processing). I assume this spec allows the TV to inform the surround processor continuously of the current picture delay.

Once upon a time I hacked something like that into TVTime (http://tvtime.sf.net) that constantly updated a delay effect I'd modified on my SB Live 5.1's emu10k1 DSP.

This is a really nice feature for whole-house setups.

Different feeds can have slightly different syncs. This is especially true with a matrix operation that uses multiple screens feeds and a single audio feed.