With my Focusrite Scarlett 6i6 I think it was setting the ASIO buffer size to the largest possible setting (1024).
I found this quite annoying, because it wasn't obvious what it was doing and it didn't set it back to the setting I had it at (256) when finished.
That's what I would have assumed, but if I recall correctly it was not doing that in my tests, as my DAC supports up to an 8192 sample buffer (which I use).
I'd have to test it again, but really the only thing that mattered for me was disabling the option.
EDIT:
Nevermind, it doesn't appear to be changing the buffer setting for my DAC at all.
I set the driver to 64 samples and Media Center for 192kHz playback, which is too low (requires a minimum of 256 samples) and I get distorted playback via ASIO no matter what the buffer size is set to in Media Center.
WASAPI buffer size works as expected.