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.
