I smoothed the bottom of the pair of shoes with foam and carbon fiber and picked up 2 watts over my old shoes. The ones I smoothed were 1/2 size larger, so it isn't a totally apples to apples comparison. It was a drag reduction for my setup.
My guess is it is never going to hurt, but don't expect huge gains either.
My guess is it is never going to hurt, but don't expect huge gains either.