He knows that, but is asking why you prefer to loop it through like this rather than using an adapter to connect RCA directly to the sound card's Line-In.
The audio output on the ATI primarily exists because it's a TV tuner. If the loop-through is truly a direct passthrough with no delay compensation added, I can't think of any advantage using it for VCR capture. Elsewhere, lordsmurf has suggested that it does provide better sync though.
You can always test it every way and let us know, Luca T... VirtualDub
has an audio waveform display to see which audio is associated with each frame.