The advantage is that it allows you to use that 3-prong boutique cable that has been coiled for months in a box in your closet. Break it out and fire it up. No promises it will actually do anything for your audio/video performance but that is the advantage.
It is up to you to experiment. Again, YMMV on this one for sure.
You don't need to use a 3 prong/conductor ac power cord with the adapter. Its far mor difficult finding a 2 conductor cord.Having the 3rd conductor allows you to move cords around to other components down the road. Make your own and save a bundle. It can make surprising improvement in both audio and video performance.