Here's the response that an adcom would probably give you:
"Why on earth would we ask for something and deal with processing it if we didn't think it was useful at all?"
And I think there's actually a good argument there. I have a feeling that, like many of the other 'soft factors', it makes a difference in two cases:
1. So-called borderline candidates. This includes nearly the entire admitable pool at schools like Yale and Stanford.
2. Truly awesome or disastrous recommendations.