The advantage is that Smashwords is promoting it - as are other authors. So you get to ride on their coattails. I will still sell more at Amazon this month then I will at Smash, but there will be new sales this week (already have been) that I would not have gotten otherwise. That is new readers for my series and that is the real goal of all of this. Connecting readers with my books for their enjoyment.
The odd thing is typically half the people will still pay full price, even though you have the discount up. I am grateful, but baffled by that.